This might be the craziest thing i have seen. I have had people run their pipe or cable through holes i drilled. I have had people use my keypad/touchpanel boxes to mount their security keypads. I have even had people use my wires. But i have never ever had anyone uninstall my device and use my cable for their device.

Bill for that service call and encourage the client to have ADT reimburse her.

Maybe keep the smoke detector and tell the ADT tech that if he wants it...he has to come and get it.