Abstract: A security listening system activated by and transmitting over telephone lines to allow listening for sounds at a remote location over a standard telephone line using a standard telephone instrument at the calling end. The system is connected at the remote site to be monitored across the telephone standard tip/ring pair either in parallel with the standard telephone instrument or in lieu thereof. The system is powered by D.C. voltage obtained by rectifying the telephone voltage or, optionally, by a battery. The unit monitors ring sequences on the telephone line and after a pre-established number, activates the balance of the device. If thereafter during a fixed time duration a pre-established tone signal of minimum duration or longer is applied to the line, the system connects a microphone and amplifier across the telephone line to allow the listener on the other end to hear what is happening in the surrounding area.