I have a scantronic 9827 displaying tr error code?

Hi Steve, tr indicates a tamper return fault. This is the part of the system which gives you tamper protection on the outside bell/sounder.

If it was working before the battery change then most likely you’ve simply pulled out a cable from the terminal. tr terminal is about 12 up from the bottom of the circuit board on the left hand side.
Should be marked tr or tamper return.

I would check this first.

Alan
May 2020