These have a 3 pin detector: Hot, Neutral, and the Tandem. How does the Tandem function work ? In other words, when the detector is activated, what electrical change occurs on the tandem wire ? Is a signal generated ? Is it switched to Hot ? Please be as specific as possible.
Also, what is inactive state of the tandem wire?
An example unit would be a Kiddie Frynetics 1235. Thanks.