A new and improved 12-volt tester is now made in-house and the two pin probes have been spaced further apart to line up with the center of each copper run in your tapewire. This makes it much easier to test each run and to locate tapewire runs hidden by wall paper.
It is a small tester for one to determine if their flat tapewire is working and provides 12 volts. It has an incandescent lightbulb attached to two needle like pins that are used to pierce the two sections of a flat tape run. If the tape carries 12 volts (either AC or DC) the light will come on in the tester.
Be sure to check out probe tester 721-1 in comparison to 721. 721 offers the additional feature to know if you have an AC or DC circuit and if DC, which is positive and which is negative.