What does the Police button do on my Vista 20P keypad?

In its default setting, the police button acts as a panic button that triggers your security system's alarm siren.

The police button on the Vista 20P is only to be used during emergencies. It sends an emergency signal is then sent to an operator at your central monitoring station who will proceed to contact the police.

You can program the police button to trigger a silent alarm instead of an audible alarm, if you so prefer. You can even set up a verification call to your house from central station as a preemptive measure against false alarms. Still, it's important to remember that the police button is for emergencies only.