Dispersing a static field from a touch circuit - escape room
There's a > 50% chance that you can fix this with a 1 MOhm resistor between each screw and the negative battery/power supply terminal of the lock box. If this somehow makes the device no longer function with contact, try 4.7 MOhm.

The theory is that the lock box capacitive sensor is measuring against ground, which is a common case, and that the static build-up needs to be dissipated there. Human skin contact resistance is usually well below a megaohm, so the magnitude of the bleed resistor seems to be big enough to not interfere too much with the circuit.

You should be able to jerry rig this with some solder, or just some conductive glue, and some bent-wire resistors from Fry's or Digi-Key or your old forgotten electronics experimenter's kit :-)