12 volt automotive type relays are dirt cheap and great for these applications. I did something similar in my own home. For example, one code opened one garage door and another code opened the other. Yet another code would override the sprinkler system's timed settings.

I used a 36 station intercom where '3' would open the one garage door '4' would open the other. Because garage doors just needed a momentary contact closure, a regular relay contact associated with each code was all that was needed. For other devices that needed to stay activated, I used a pair of SPDT relays per code, one to perform the switching of the device and the other to latch on the power to that relay. For example, the code for the sprinklers was '5' and when dialed, it would send power to both relays. Through NO contacts on the second relay, power was applied to the controlling relay constantly upon activation. '25' would fire another relay that dropped power to the 'ON' relay pair.

1A2 lamp power supplies are fairly common to provide 10 volts AC. I just sent this output to a 2 amp full wave bridge to convert it to 10 volts DC, which was ample to activate a 12VDC automotive relay. Relays and diodes can turn 1A2 intercoms into magic boxes in no time.

Ed Vaughn, MBSWWYPBX