Most stable 2 wired system ,best chips ,excellent call effect ,most popular & unique apperance.All certification approved Features and Advantages1. Latest chips, clear intercom effect2. Intercom and unlock when someone call at the outdoor3. Pich up the indoor phone, press "TALK" buttom to speak to the outdoor when standby4. 2-wire system, Easy installing.5. 2 Buttoms, Easy operation. 6. Nice ...