Is it feasible/worth it to recover an alarm system keypad that is unreliable?
These types of keypads have a rubber membrane with the buttons on one side and conductive material on the other placed above a circuit board with contacts.  Crud or oxidation can build up on the back side of the buttons or on the circuit board and cleaning it can often help and get you some more years of use out of it.

Generally they are easy to disassemble and you can clean the back side of the buttons gently with a damp cloth and the circuit board with some compressed air or some circuit board cleaner.

As far as taking it off, you will probably need to take it off the wall first, then find the screws that hold it together or the latches that hold the case halves together.