Sensor
a device that detects a change from one state to another. For example, a door/window sensor detects the change in a circuit from a normally closed state to an opened state.

Silent Alarm
an alarm received by a central station operator which does not activate a local alarm sound.

Smoke Sensor
a device of either photoelectric or ionization design which detects the presence of smoke and sends a fire alarm signal to the control panel.

Spatial Diversity
using two or more antennas (on either the transmitter or the receiver) where the two antennas are switched. Having antennas with unique locations provides independent signal paths through space and thereby significant fade resistance.

Supervision
the use of a special signal sent automatically from the transmitter to the receiver to inform the receiver that the transmitter is operating properly.