The GEM-WP is an single function pendant/keychain transmitter compatible with all Gemini and NAPCO Express control panels when used with the appropriate wireless receiver. The GEM-REVC-XP8 is compatible with the NAPCO Express Series and GEMP400 & P800. For all other Gem series controls, the GEM-RECV8, GEM-RECV16 or GEM-RECV96 are compatible. It serves as an emergency device for use as a police panic and/or auxiliary emergency transmitter. Two replaceable Energizer 386 1.5 V, Silver Oxide Cells power the GEM-KEYF transmitter. A flashing LED indication signals a low-battery warning to replace the batteries. To operate simply press the button momentarily. Note: The button when pressed will transmit the respective signal to the Central Station. The LED will light while the unit is transmitting. Low-Battery Check. The batteries are checked automatically during any transmission. A low-battery condition will cause the LED to come on for twice the normal time, then start pulsing about once every 1.5 seconds; a low-battery report will be sent to the receiver.