Circuitry schematics for Taser-like devices are not easy to come by. However, it can be ascertained from a review of the literature that the basic circuit developed by John Cover is essentially based upon a high frequency switching power supply design. A DC source (9-volt battery) is first converted to quasi-AC (more like pulsed DC) using switching transistors. The switching frequency is usually in the range of 200 to 500 kHz. Since the circuit has no reference to ground per se, it produces roughly 9 volts peak-to-peak. This voltage is then fed into a step-up transformer and converted to a much higher voltage. There may actually be more than one step-up stage as well.

The output of the transistor oscillator is fed to a charging capacitor. It is the value of the capacitor that determines the period (and frequency) of the pulse that is generated. Backtracking for a bit, the pulse frequency is the most important aspect of the efficacy of the Taser-like device. The pulse frequency, according to Cover, must be between 1 and 20 pulses per second. Whether this was the basis of his "T-Wave" patent is uncertain. Why the seemingly arbitrary pulse frequency? According to the Cover (1968), this pulse frequency range produced the desired "subduing" effect. Cover discovered this by trial and error, at least according to his anecdotal paper (which led to the patent). Why not 60 Hz as this frequency appears to be closer to the resonance of the human body? Apparently that would have put the device into the gray area insosfar as non-lethality was concerned (Cover, 1968).

The newer, high voltage units use two 9-volt batteries. Most likely, the batteries are placed in parallel to provide enough output current when the initial voltage is stepped up to an even higher output voltage than the older models.

The current produced by a 9-volt battery is limited and will vary with the load impedance placed across it. Ultimately, when the output voltage is stepped up through the transformer, the current decreases proportionally as per Ohm's Law. Higher and higher output voltages mean less available current.

The output voltage is proportional to the load impedance, given constant current. That load impedance is the human body. Exactly what level of voltage is necessary to permeate the human body is unclear. The resistance of human skin is 500K ohms when dry and will lower to about 1K ohms when wet. The internal resistance of the human body, however, is between 100 and 500 ohms.

As an aside, the necessary voltage to penetrate the human body must be much higher than 12 volts DC. For example, a car battery can generate tremendous amounts of current but it has no effect on the human body. That is because the voltage potential is too low. We know that 120 volts AC can easily permeate the body. So, why do we need 500,000 volts? And, do the devices really produce the advertised voltages? Stratbucker & Marsh (1995) indicated that some of the Taser-like devices produced beween 50,000 and 80,000 volts into a set 20,000 ohm, purely resistive load. Oddly, using Ohm's Law, this implies that the device can produce roughly 4 A of current. That can only be true if time is taken into consideration. In other words, that amount of current may be available for a significantly small fraction of a second. Or, the output voltage across the load will drop significantly.

Before going further, one thing should be made clear. The amount of current (in Amperes) that is fatal to humans is also a function of the associated voltage. Some Taser-like devices operate at about 3 mA, far too low to be lethal. The majority of devices probably produce less available current. Overall, this may also be too low to be effective although current as little as 30 mA could prove fatal.

The electrocution potential is further limited when the nature of the pulse is considered. Each pulse is composed of a burst of high frequency AC, so the actual power dissipated to the human load is even lower than if it were a pure pulse. Power must now be calculated using the root-mean-square (RMS) method. Essentially, the output of any Taser-like device is almost analogous to a 250 to 500 kHz carrier being modulated by a 17 to 22 Hz signal.

Nova USA claims that it is the only Taser-like device manufacturer (aside from licensed Taser vendors) whose product really works. Its corporate Web site indicates that its devices are "calibrated for maximum takedowns." How so? There really is no way to calibrate the circuitry described. In fact, it can be assumed that the pulse frequency will vary depending on the actual impedance of the human load. Essentially the transformer output coil, the charging capacitor, and the human load comprise a kind of crude RLC tank circuit. Nova claims that its circuitry is patented. Nova is a licensee of the Taser T-Wave technology. Interestingly, Nova cautions customers to not purchase any of the cheap imports because the latter do not work.

Could it be that there is nothing proprietary about any Taser-like device? Do they all work, or do none work at all? There appears to be nothing special about the circuitry of these devices. The concentration on output voltage has further minimized the output current. That current is essential for the disrupter signal to permeate the whole human body in an expedient manner. The higher voltages also will produce more initial pain upon contact which is not conducive to subduing the recipient. In addition, the instantaneous shock will repel the recipient almost immediately, which further deters from that objective. The Taser-like device was not intended to be a cattle prod. Subduing the recipient requires that enough contact time (6 or more seconds) is allowed for the pulse frequency to disrupt the nerve firings of a major portion of the human body. The electric current will move from the initial contact point throughout the body, but not instantly. Remember the last time you were shocked by house current? The effect of the 120-volt house current can be characterized as gradual incapacitation. Only the throbbing 60 Hz frequency produces awareness of the electric shock. There is usually no pain accompanying the numbing paralysis. The short-term pain from higher voltages may only serve to anger the recipient.

The only true benefit of higher voltages is the device's ability to pass the current through layers of clothing, at least according to Air Taser promotional data. Clothing can act as an insulator especially at lower voltages. In other words, the higher voltage potential has the ability to pass through some insulators.

Incidentally, there are no specifications as per any standard available for these products so comparisons will be difficult to ascertain. The high value of skin resistance suggests that the higher voltages are necessary to permeate that barrier, especially given the fact that the working current is so low.

Finally, it is difficult to take seriously the large number of Taser-like devices on the market today. Names like Muscle Man, Stun Master, Z-Force, StunZilla, Thunder Force, etc. do little to invoke confidence in the products. Upon closer scrutiny, most devices are identical with the exception of the name plates. The packaging often reveals nothing about the contact information for the manufacturer or how the overstated (e.g., "lifetime") warranties would be honored.

And what of the various claims of proprietary technology? What about "patent pending Phase Induction" technology? "Pulse Watt" technology? "T-Wave"? "Electro-Muscular Disruption" technology? The names mean absolutely nothing as if they were formulated by some bafflegab generator. In effect, the technological aspects of Taser-like devices should all be extremely similar. None have Star Trek capabilities. None use laser, sonic, RF, magnetic, or microwave technology. They all rely upon high voltage and low current emitted as a low frequency pulse. Extended contact must be made for the device to be effective. Air Taser's high effectiveness has to do with the contact probes which attach to the body. Most times skin is broken so perfect contact is made. Other devices must rely on the user to press the device as close as possible to the recipient for an extended time.

And, what of the foolish looking contacts that arc? Do they serve a purpose? The original Nova XR-5000 had them, so all imitators should have them. They do serve several purposes:

• Intimidation
• Testing
• Discharging

The use of premium batteries (e.g, commercial grade alkaline) is a necessity. Even a cheaper, generic brand of alkaline batteries may compromise the performance of the Taser-like device. Many of the scathing and purely anecdotal reviews of Taser-like devices may not have taken this into consideration. One anecdotal review by Cook (1997) was somewhat positive. Most of those reviews are circa 1996 and the test conditions were not standardized with control parameters (e.g., type of batteries used, whether fresh or not, etc.).
 

The common citizen has no rights. This is, in fact, the paradox of the Taser-like device and all other security products. Security devices should not be deployed until one is absolutely sure that it is necessary. In other words, the concept of deploying a security device from a "safe" distance may be ludicrous at best. For one thing, what assailant is going to announce his intentions from 15 feet away? An assault would more than likely come from behind, ambush style. Any other style of confrontation is just an exhibition of stupidity (i.e., machismo, etc.).

This issue may be of primary consideration when purchasing any device used for self-defense. What good is an Air Taser or pepper spray when the victim is ambushed? Use of pepper spray at that point in time will disable both the assailant and the victim. The Air Taser requires at least 6 feet of distance to be effective (unless one can eject the probe cartridge expediently and use the device to stun the assailant).

Self-defense, then, can only be justified when one is already being accosted. Therefore, the Taser-like device is a viable apparatus. It may be the only viable apparatus. Within close quarters, other deterrents such as pepper spray, a gun (e.g., the "nine"), or other devices may be totally useless. At a useful and safe range, these devices may also be considered "excessive force." Why? Because the assailant has yet to commit any act that could be deemed serious enough to that justify the use of such a self-defense device. The assailant then becomes the victim. Guess who will be arrested?
 

The Nova line of "electronic defense units" is said to set the benchmark for all Taser-like devices. Nova itself urges all prospective buyers to "beware of imitations." LoserNet Labs acquired a Nova Spirit "White Lighting" model. That's not a spelling error. That's how the product was branded in gold letters on its white case. One has to wonder when a device goes into production with little quality control.

Like all other Taser-like devices, it is constructed similar to a cheap flashlight, but its $149 price tag is exorbitant. One noticeable difference is the embossed patent numbers (No. 4,162,515 and 4,255,132) which are proudly molded into the plastic case. Aside from that, the Nova looks very similar to all other Taser-like devices, right down to the arcing test probes.

The Nova instruction manual did clear up a few things. The proper choice of batteries was emphasized. And, the estimated life of an akaline battery was about one minute without any noticeable degradation of performance. The Eveready Energizer battery was the battery of choice for the Nova Freedom model. The Nova Spirits use a proprietary lithium battery pack. Replacement cost is a steep $22 on average.

Unlike the "imitations," there have been no negative reviews about the Nova line. The Nova "electronic defense units" (as Nova calls them) are still in use by many law enforcement agencies. The Washington Association of Sheriffs and Police Chiefs (which has it policy manual on-line) labeled the device a "true weapon" and mandated that officers treat them as such.

The Nova instruction manual is somewhat ambiguous about the product's incapacitation ability. "The Nova is effective on the majority of assailants," the manual reads. However, the Nova manual is a little more explicit about the effects at various exposure times to the device as opposed to that of the "imitations." The Nova manual reads, "A full contact blast of 5 to 7 seconds can immobilize an attacker," whereas the cheesy brands have opted to claim, "Over three seconds will cause loss of balance and muscle control, mental confusion and disorientation." Who do you believe?

A check of the patent numbers mentioned earlier yielded some interesting information. Patent 4,162,515 is for a portable (i.e., battery operated) shock device based upon earlier patents of various electric cattle prod devices being pulsed by a stator-type switching unit. Patent 4,255,132 is the end result of Cover's (1968) work. The device described is currently called the Air Taser. Aside from the description of the projectile mechanism, Cover detailed the theory of operation of the circuitry (later called "T-Wave" technology). The circuitry is the basis of all Taser-like devices. Typically, it's a crude DC to quasi-AC (pulsed DC) inverter which then uses a charging capacitor to pulse the ouput to the external contacts after being stepped up in voltage by a ferrite core transformer. Cover also detailed the use of another capacitor to aid in stabilizing the output resonance of the circuit.

The effeciveness of the Air taser and Nova XR-5000 is documented. There are also extensive medical studies. The efficacy of the devices may well be because the peak output voltages (unloaded) of the devices were limited to about 50,000 volts. Naturally, the true output voltage would depend on the load impedance. Thus, the only difference between the lower voltage models and the higher voltage models is basically the number of windings on the step-up transformer's secondary coil. This would not merit the $20 to $60 increase in price. Theoretically, the higher output voltages means less current is available. Doubling the output voltage means half the current. That is, if that current was available in the first place.

Using Ohm's Law, it is easy to see that 4 ma at 50,000 volts produces about 11 watts of power. If that's true, then the DC source at 9 volts must be able to provide a minimum of 1.2 A of current. Remember, all values are peak. However, the actual current will be limited by the output current capability of the oscillator transistor. This is all feasible given that a 9-volt akaline battery can provide high current for a brief period of time. The higher output voltages will require even more current from the battery if the target 4mA output is desired. A point of saturation will occur and the available output voltage will drop across the load.

Overall, there appears to be no reason why the Nova devices should be better than the cheap imitations. The patent hardly seems enforceable since there is nothing really proprietary about the device. That probably accounts for why there are so many imitations. The overall cost of the raw components is about $6 for OEMs. The only real benchmark is the current output specification of the oscillator transistor. In other words, that is the only way of telling whether the device can provide enough output current to be effective.

As for the pulse frequency, there seems to be a wide variation. Nova claims that its devices operate within 17 and 22 pulses per second. Air Taser specifies about 12 to 15 pulses per second. The patent filed by Cover specifies a pulse frequency between 1 and 20 per second. The pulse frequency is determined by a single charging capacitor. There are no elaborate timing circuits. As long as the damned thing pulses, it should work. However, it must be concluded that the effective output current is the most important parameter. LoserNet Labs believes that all Taser-like devices are extremely similar.The choice of fresh, quality batteries is the most important criterium. One crude method to test for output current is to measure the amount of time before the batteries are depleted. Even test firing the device consumes power. Nova's XR-5000 Freedom model will operate properly for one minute of total firing time off of a fresh 9-volt alkaline battery. That's probably accurate for 3 mA output. The off-brand models that use two 9-volt batteries should deplete the batteries within two minutes. If the batteries last much longer, there is a good chance that the device is a joke. The output cuurent most likely will be in the uA range. Totally useless.

Nova has made a name for itself because it was the first hand-held Taser-like device. It was made in the USA which gave it more credibility with domestic law enforcement agencies. The same applies to the Air Taser. Medical research and documentation further provided credible evidence. Yet, there is nothing high-tech about the device. Of course, it is hard to discredit the Nova line. There are no false claims. Several models have had extensive use out in the field in actual law enforcement situations. Nova's Web site accurately describes the device's application as that of "intimidation and subduing." The Nova appears to be best of the Taser-like devices with a proven track record, that is, if the high cost can be justified.