My question is this. Are all the biscuits in an 11-20 blue-pack (as above) the same, apart from the numbered stickers, or is the internal wiring different?

I ask because I've just broken a No 20 while attempting to replace a doorbell plate.

Can I use another biscuit from the same pack as a replacement, or will this upset my alarm system?

Sorry if this is a stupid question, but I'm no expert. I've asked for high-priority because my house alarm is disabled by the problem.

If this is programmed as 20, this will need to be another 20 as a direct replacement.

The resisitor in each one is different, so you will need to reprogramme or use a new number 20, as above