That wasn't exactly my point, but I understand where you are coming from.
How can you prove that the supply and cable is ok before you bin the detector without your meter?
You have to do your best to prove the equipment/cable after a F/A. Many seem to blindly swap it out and feck off.
I'm sure I have mentioned before I have been to calls were three different engineers had been and swapped the same sensor after false alarms over a month period not even thinking to check for a cable fault.
Look at it from both ways. If you don't find an obvious issue you are normally best to swap it. You will be back again, if there is an issue, but this time not earning anything.