The alarm will not work at all.

1.	The first thing to check is that the alarm is switched on and that there is power across screw terminals 1 & 2. The "power" LED should be lit. The polarity of the power source is not critical.
2.	Assuming the power supply is OK, press one of the "alarm tone test buttons" and see if you get a signal from the speaker or if the strobe light flashes. If this is OK, the problem is probably with the exchange line connection or with the device used to trigger the alarm.
3.	Check that a T200 (or a buttinski) will operate when connected to the cord you plug into the alarm's modular socket. If the T200 won't ring on an incoming call, the input ring signal is not analogue and the alarm will never work in that situation.
4.	If there is no alarm tone when a test button is pressed in step 2, turn off the power source and place a multimeter on it's ohms setting across screw terminals 7 & 8. You should see the speakers voice-coil resistance. If you don't, check the speaker and/or the speaker's cabling for an O/C.
5.	If you can see the speaker's voice-coil resistance, it's possible that the volume potentiometer has been damaged. Test it with this procedure