Glad you back Paul, really did miss you
Happened many times, I'm more than happy to send a man & an invoice... but I've always asked people to be certain the beep is coming from the alarm & not smoke alarm.
Personally I've had been told there's no smoke alarms in the house only to attend & find a pair still in the packet from B&Q which have being waiting a couple of years for the home owner to fit
Found a "Free" British Gas Co3 alarm in roll top desk, beeping with low battery,
I also get lots of OAP's complaining about the "Free" battery powered smokes beeping (fitted by the fire brigade)
Couple of hundred quid to renew a basic house alarm on the old cables
Smoke alarms have a recommend life of 10 yrs, to replace a pair of mains powered smokes cira £100 as booked work