It seems like a bad idea to directly connect long alarm lines directly to MCU pins.
The diodes sold for protection don't appear to be implemented correctly.
At a minimum you would want reverse biased diodes between the pin and each rail (GND and 3V).
Better would be that in addition to a series resistor and a capacitor to ground.
Am I being over paranoid? Have people have units fail unexpectedly (assuming most likely cause is ESD), or is this thing strong enough to take the ESD from long wires strung around the house?
Here is a good discussion on the issue and the possible solutions.