The tester is designed to tell you whether or not your outlet has power, and whether it's wired correctly or not. It couldn't be easier to use -- just plug it into an outlet. The only limitations on this tester are that it won't work with non-grounded (two-wire) outlets, because it has three prongs on it, and it is only made for use with 120-volt circuits.
The tester has three lights, and depending on the condition of the outlet, some, all, or none of them will light up. The legend that tells you what the different lights mean is printed right on the front of tester, and it is pretty specific. For example, rather than simply telling you that the outlet is wired wrong, it will show you whether hot and ground are reversed, whether hot and neutral are reversed, or even if one of the lines is open.
It is small enough to fit in the palm of most people's hands, and it is lightweight and very portable. The tester makes a great troubleshooting tool for copier and printer technicians -- as well as anyone who's working on a device that runs on 120-volt AC power -- to help determine if an electrical problem is internal or external to the device. While it can't give you an exact reading like a voltmeter or multimeter can, or display a quick fluctuation in voltage, it will show you at a glance whether or not the outlet is providing the correct power. And since it plugs right into the wall, it doesn't require batteries. For very specific line problems, the tester is no substitute for a multimeter, but it is nice to have as an extra tool. For what it's meant to do, I would give it 4.5 out of 5 stars.
This specific Sperry Instruments tester isn't currently available online, but you may be able to find it (or a similar one) at your local hardware store. It looks like an electrical plug set into a squarish piece of yellow plastic, and it shouldn't be any more than five bucks. You can also get a GFCI-compatible tester -- it performs just like the standard tester does, but it can also test (and reset) GFCI circuits.
(Originally published on Helium.com, April 2010)