When visitors arrive, they press the call button and the device places a high-quality call to up to 2 numbers announcing their arrival. If the person answering the call wishes to allow entry, they simply press a button on the handset of the phone which releases the onboard relay. Allows 200 phone numbers toll-free to call the system, triggers on-board relay to activate gate Not only does the system provide two-way voice, but caller ID access control allows known numbers to call the unit. When the call arrives, it hangs up immediately, and if the number is known, the door is released. for using a mobile phone instead of a 'key fob' as up to 200 users can operate the gate this way. Easy to install, set up and operate, you can press a button on your phone's keypad to release the door opener for visitors, even while on a call., Manufacturer: MNMIOIO