Shock Tactics, Part II

TENS machines are generally designed to emit a regular series of short pulses of electrical current and even the simplest one will give you the ability to turn the pulses on and off and to vary their strength, otherwise known as amplitude or gain: the higher the amplitude, the more intense the sensation, though of course the total effect will vary according to where on the body the pulses are applied. Look for a machine that has a continuous control like a knob or a slider for this latter job, rather than a series of preset levels: subtle variations in intensity can be enormous fun.

Another way of varying the intensity of sensation is by altering the duration of each particular pulse, and some machines give you that option with a pulse width control. Very short pulses, say of under 50ms (milliseconds, or thousandths of a second) will hardly be perceived, from 50ms upwards they become quite marked and definite, and above 250ms they are starting to get too long to be useful. I usually stick around 200ms. Amplitude and pulse width interact with each other and if you have a longer pulse width you will need less amplitude to have the same effect.

The next critical variable is the speed at which the pulses recur, known as the pulse rate or frequency. Some of the cheapest boxes have this preset but I'd advise that for any decent fun you need a machine that at least allows you to vary it in a useful range. At 2Hz (or two pulses per second), the pulses come slowly enough to appreciate each one individually but are fast enough to be relentless and insistent. As you increase the rate each pulse becomes difficult to distinguish, and the overall effect becomes more intense, with less recovery time for the body between pulses: you may find that if you started with an amplitude that made the bottom ouch at 2Hz, he or she will end up screaming at 30Hz where the pulses are merging into a continuous prickly tingling. Past 150Hz, the response seems to change again: all sense of discrete pulses has gone and the feeling is a constant shimmering, becoming more bearable as it increases in frequency. Some TENS machines have special high settings of 10KHz (10,000 pulses per second) or more, which even at high amplitude levels are barely perceptible: while these may be useful settings for someone who is trying to reduce unwanted pain, they are not much use in SM play!

You will also notice that the pulse width and the frequency interact: at higher frequencies you will need to keep the pulse width short enough to ensure there is still a distinct gap between each pulse. Simple maths tells us that at 100Hz, for example, pulse widths above 10ms will result in a continuous current. As is often the case with sensations, marked changes are what makes all the difference.

The better machines offer other options. For example, my machine (a V-TENS Plus from Body Clock in London) has four different operating modes. On Constant, the pulses are emitted continuously, in Burst they come in approximately one second bursts with a second of silence in between. Modulation Mode 1 is the most interesting: here the pulses increase and decrease in amplitude over a two second cycle. The brief periods of relief and the inevitability of the returning sensation are particularly effective in play. Modulation Mode 2 does a similar job for pulse width but I have found it much less useful. Though the preset rates of these bursts and modulations are well chosen, a machine that allowed you to vary them would be a further improvement. These different modes are offered because when using the machines for pain relief some people report a dropping off of effectiveness after a length of time on one setting. By varying the sensation, you overcome the body's tendency to adjust to the machine — this facility could be useful in a perve setting too.

How do the pulses make the jump from the machine to the skin? As explained last month, for electrical energy to travel effectively it needs a good conductor. The more conductive the path between the machine and the bottom's body, the more efficiently the machine will work and the more intense the experience will be. And there are also practical considerations to bear in mind.

Ordinary basic cables of the sort used for doorbells or cheap audio leads will usually form the main length of the signal path. You need two cores, one for the outgoing signal and one for the return path to complete the circuit. Some cheaper units have cables that are hard-wired into the box, but sockets with detachable cables give a sturdier and more flexible system. Mine uses 2.5mm (1/10") mini-jack connectors similar to those use for headphones on portable hi-fi: these are readily available from electronics shops so you can make up your own leads and contacts. Cables will normally be 1-1.5m (3'-4') in length, and need to be of a kind where the cores are joined along most of the length but can be separated at the business end so any contacts you use can be placed a reasonable distance apart.

It's when we reach the other end of the cables and the contact point with the body that the fun choices come into play. Obviously the contacts must be conductive, and make good contact with the body; you should also bear in mind that the smaller the point of contact, the more intense the sensation. Within these concerns, there are many possibilities, but in almost all cases, conductivity gel will make a big difference. This is a non-allergenic, water-based lubricant sometimes supplied with machines and also available from medical suppliers. It is similar in consistency to lubes like KY and in fact you can improvise your own cheaply by mixing KY with ordinary table salt. Try using 1/3 of a teaspoon (2ml) of salt to 2 tablespoons (30ml) of lube. Always clean it off toys after use to avoid corrosion.

The cables normally supplied with TENS's end in square silicon-rubber contact pads about 25mm (1") square: you will probably find that the pads are detachable and the leads actually end in two simple metal plugs that fit into the pads. To use, spread the pads thinly with gel and place flat on the skin, sticking them into place with micropore dressing tape (available from pharmacies). Because the contact area is quite large, the sensation can be diffuse, but these pads are not without their uses.

An alternative is to use salt water to make ordinary cloth conductive. A correspondent of mine suggests saving the elasticated tops off old socks for this purpose: soak them in salt water, wring them out well and use them to hold either the pads themselves or the little plugs that fit into the pads in place. Again you will be creating a diffuse conductor with a large surface area.

A more flexible arrangement is to use leads terminated in crocodile (alligator) clips. Some TENS suppliers have these leads as an option but if you can wield a soldering iron you should be able to make up your own for the cost of a few cheap components. The small insulated variety are best. In most cases you won't want to attach these directly to the skin but they are the easiest way to recruit other toys into service as electrodes: piercing jewellery, metal cockrings, clamps and sounds, for example. In these cases the sensation will be more concentrated by the smaller contact area.

Whatever you do, be very careful not to let the electrodes touch each other when the TENS is running. This will create a short circuit and will most likely blow your machine.

There are all sorts of other wicked ideas for contact points and electrodes and we will discuss a few of them below.

Most people know that if you want to run two sets of speakers from one hi-fi amp, or, even less advisedly, two appliances from one wall socket, you can bodge it by connecting the two sets of leads to the one output, an arrangement known to electricians as connecting in parallel. With TENS units things aren't quite so simple, since the body is also part of the circuit. If you attached two sets of leads from one output to the same body (or even two bodies touching or otherwise connected), the electricity would still only take one path — the shortest path through the body and back to the machine. One reason this is inadvisable is that it's best to know exactly which path the electricity will take so you can make sure that it's a safe one.

If you want to run two or more sets of contacts you either need extra machines or a machine with more than one channel. Genuine multiple channels should be electronically isolated from each other, so that the current sent out over one channel will not return via the other. You can check this easily: hold two contacts from one channel in the same hand so that they are not touching (pressed between two different pairs of fingers is the obvious method) and turn on the TENS so that you can feel the current flowing. Drop one of the contacts and the sensation should disappear. Now connect a second set of contacts to another channel, again being careful not to let them touch each other, and, still holding on to one of the first channel's contacts, place one from the second channel where the dropped contact from the first channel was. Then try with the other contact from the second channel. If the sensation returns as a result of either of these actions, the second output is ! not a true separate channel and should not be used.

When choosing multi-channel machines you may also want to check how independently each channel can be controlled. My machine's two channels have their own amplitude controls, but the settings for frequency, pulse width and mode are the same for both. A more sophisticated machine may offer more flexibility.

The first thing you may have to overcome in play is fear. If you're playing with someone who is new to electricity and deeply fascinated but also scared, it might be an idea to show them how to use the machine then leave them to experiment on their own for a while. You may be surprised to come back and find the machine on maximum!

Tops who are electrical virgins are best advised to experiment on themselves first until they get to know their machine and what it can do thoroughly, a process that should be repeated each time you get a new machine, a new accessory or a new technique. You may not drive the machine as hard as you'd drive it on your bottom, and you must also remember that different people have different thresholds, but at least you will have some idea of what the settings and configurations can do. And in all cases start at low settings and build up slowly.

One way of using a TENS is on muscles. Peter Boots, in his introductory article on TENS play, suggests 'a good place to start exploring is the legs. Try putting one terminal [a lubricated contact pad] on the inside of your thigh about 8cm (3") from the crotch, the other one on the inside of your ankle. Then experiment with the various settings of your unit, always with the unit turned off at the beginning. A good start is to set intensity to about one third of maximum and then to dial in various pulse rates and widths of signal to experience the different sensations. Next choose approximately 40% pulse rate and signal width and increase intensity. You should feel either calf or thigh muscles respond by contracting (twitching) in rhythm with the pulse setting. You may need to adjust the position of the pads slightly or check for good contact if your muscles do not respond.

When you reach an intensity level at which your muscles contract comfortably, increase the pulse rate until you reach a point at which the pulse rate is too fast for your muscles to react — they will cramp instead. Depending on your point of view this can be either unbearably painful or an incredible turn-on. Next try putting a pad on each ankle — really nice. Then try putting one or both pads on the sole of your foot. Lastly, if you have two sets of outlets, put one set of pads on each leg.

From here on it's plain sailing. If you can't remember basic human anatomy from school biology, take a look at a fitness or anatomy book at the library and see where all the leg, arse and stomach muscles are located. The principle is really simple — place the contacts a little beyond where muscles connect to joints and tendons.'

There is one special safety consideration when using a TENS on muscles: if you are using bondage, allow the limbs you intend to work on plenty of room to move. If you force a muscle to spasm when it is held in place with severe bondage, you may cause serious strains and muscle damage.

If playing with muscles is not your game, you may prefer TENS torture on sensitive non-muscular sites. The genitals are the obvious ones, and quite safe, though you may need to adapt your contacts for maximum effect. The supplied contact pads may be useful across labia and balls and on the shaft and head of the penis (though peeling off the micropore tape may feel uncomfortable on some of these sites!). Various steel rings can be pressed into service on the male genitals by attaching crocodile clips. Another suggestion is to obtain from a hardware store one of those old-fashioned scouring pads made out of copper wire, unpick it into a copper net and use it to envelop the balls. Copper wire is in any case a useful item to wrap around various body parts.

A poster on Usenet once suggested creating a moving electrode by ' connecting one side of a circuit to a large electrode on the lower back and taking a Q-Tip swab [cotton bud], and wrapping a couple of turns of copper wire connected to the other side of the circuit around the shaft where it joins the cotton tip. You then can wet the swab with salt water and draw points and lines of tingling or pain on the legs, stomach, back, and genitals. Depending on the current level (this is a good one to try on yourself first) it can feel like a tiny vibrator or like you're flaying the skin with a sharp knife (but leaving no damage, marks or sensation of cuts behind). This can be especially intense for a subject who is blindfolded and doesn't know what's happening — the sensation is quite outside most people's frame of reference and they have no idea what you're doing to them.'

A word of caution: be very careful where you place the Q-Tip, bearing in mind the need to avoid current across the chest. Keep it well below the ribs and do not place it anywhere on the arms if the other terminal is at the base of the spine.

Another obvious thing people think of is using electricity with insertive toys. You can use one toy to carry both terminals, and then leave it pulsating in a bodily orifice: a US sex store makes a plastic egg with one terminal as a band around the waist and the other a pole that runs from top to bottom, which is very effective placed in an arsehole or cunt. Alternatively the toy can be used as one terminal and the other placed elsewhere. This is very effective with men if one terminal is a dildo in the arsehole and the other an attachment on the dick or in the space between the base of the balls and the arsehole, since the current then flows through the sensitive prostate gland.

Unfortunately most ordinary insertive toys are made of insulating materials like rubber, and conductive ones have to be made specially out of materials like steel and acetate: this means they come at a high price, and are also of dubious legality in some places because they can be classed as electrical torture devices. Conventional toys can be converted by attaching strips of metallic foil or copper wire, though please be very careful to avoid sharp edges.

A DIY solution is suggested by Peter Boots: 'An aluminium (aluminum) cigar tube can be wrapped with some electrical tape at the base to leave just about 8cm (3") of contact. Fill with plaster of Paris for weight and stability. After the plaster has set, attach one of the electrodes, lube well and push up the arse — make sure it doesn't disappear all the way!'.

With any contact placed inside the body, the best advice is to start very low and build up very slowly.

Clips and clamps can be used with electricity but remember that the sensation of the current will be exacerbated by the intensity of the clamp, and it is best to be careful and perhaps avoid very nasty and tight clamping. As with insertive toys, one clamp can carry just one terminal or both. In the latter case the current will be passing across the small amount of flesh inside the clamp and will be very concentrated.

If both terminals are on the same clamp they must be electronically insulated from each other or a machine-damaging short circuit will result. Such clamps can be obtained purpose made (again at a premium) or improvised using materials like insulating tape, copper wire and foil. One cheap suggestion is to use wooden clothespegs (clothespins) and either place thumb tacks through the ends with the broad heads of the thumbtacks inside the clamping area of the peg, or wrap the clamping areas with foil. Some cheaper wooden pegs might simply split if you try this, however, and you must be very careful not to short the machine out by allowing them to close together when it is on.

Some people wonder if electricity may be safely applied to nipples. While it is certainly dangerous to attach a terminal to each nipple, it is probably safe to pass a current across a single nipple by using a clamp to carry both terminals. Some people prefer to be hyper cautious and only do this to the right nipple, which is furthest from the heart.

Electricity and piercing team up superbly. Permanent piercings make splendid sites to connect crocodile clips to, especially on genitals — though avoid using nipple piercings except between two piercings on the same nipple.

Play (temporary) piercings can also be used. As well as genitals, you can use play piercings thorough the surface skin to stimulate large areas of the body, say on the buttocks, stomach and thighs, and create temporary double nipple piercings too. Remember that the piercing site will be slightly sore, and this will further intensify the sensation. To maintain hygiene, attach the croc clips on the outside of the piercing, not on the side that will be drawn back through the wound when the piercing is removed.

One minor consideration here is the tendency of metal to heat when a current is passed through it. At the tiny levels put out by a TENS you should never find this a problem, but units with a higher output (perhaps older devices) may be different. If a needle or a piece of piercing jewellery starts to heat, turn the current off immediately: a burn on the inside of the body is not normally welcome.

In conclusion, here are some contacts that may be of use to get you kitted out: all of them should do catalogues which you should obtain before you make a decision. I must stress these are not particular recommendations: I am very happy with my Body Clock unit but I haven't had a chance to do systematic comparisons with others. If anyone knows of any other suppliers, please email me with the information and any comments, since I hope eventually to build up a comprehensive resource list.

In Britain at least, the machines are subject to 17.5% Value Added Tax (VAT) if bought within the EU. If, however, you declare you are registered disabled or a sufferer from chronic pain, you may be exempted the VAT. A US correspondent who supplied the CommuMed address suggests looking at ads in the trade journal Advance for Physical Therapists for other suppliers.

• Body Clock Health Care, 10 Eastwood Close, South Woodford, LONDON E18 1BX England. Tel +44 (0)181-532 9595, fax +44 (0)181-532 9551 — Machines from around GBP40 (US$60) to GBP90 (US$135).

• Health Care Associates (MC), Premier House, Hinton Road, BOURNEMOUTH BH1 2EF England. Tel +44 (0)1202 299277 — Machines from GBP50 (US$75).

• CommuMed, 120 Kedron Avenue, Holmes PA 19043 USA. Tel +1-800-848-5397, Fax +1-215-586-5100 & mdash; Machines from US$63 (GBP42).

Next Month: Violet Wands, other electrical devices and links list.

Des de Moor is the editor of one of the web's most exciting and ambitious BDSM sites, The Deviants' Dictionary, an attempt at a comprehensive "encyclopervia" of SM terms.

Based in London, he has another life as a polemical singer-songwriter , performance poet and host of Pirate Jenny's Musical Cabaret Club, details of which he also splashes liberally about the web.

He prefers rubber to leather, shaved to hairy, and Doctor Martens to biker boots and plots devious and twisted SM encounters while going on long country walks.