To be fair if he is storing guns its probably a Police requirement that the system is monitored and maintained. We look after quite a few sites with gun safes I cant think of one that's not G5 monitored.
As above cancelling the contract wont stop the alarm from sending out test calls daily. The alarm company would have stopped taking any notice of the signals. We used to retain ownership of the monitoring equipment back in the day and then charge the customer for us to collect it if cancelled. I can see why now.
Speak to your landlord they will have to call someone out for you, they have a duty of care. If they havent bothered with having it serviced its their responsibility
Its never to late to contact engineers, alarm companies run 24/7 for exactly this reason. If your alarm was installed after 97 it will only sound for 20 mins, if it was after 2010 just 17 minutes
There is a difference with what I import to the tat that Yale imports, those panels are made by Unifore and rebadged we looked at importing them even purchased a couple of samples. But they were a pile of rubbish