As above converters are not designed or tested for this purpose. It may work 80% of the time but may not when actually needed. You need a communicator designed for ip or gsm
You can use either the HKC with standalone contacts in enclosures eith HD external contacts
or the pyronix enforcer.
Both will function without internet but notifications wont be possible,
Note our products are designed for professional installer use
It sounds like you have either a failed controller or pir.
DIsconnect all pirs andding one of them (test each one) and see if the fault disappears. If so start adding pirs back into the system until the fault reappears
Honeywell Galaxy ASK Keyprox Proximity FOB [YXO-0020] - £5.39 : | Best Price Promise | Security Warehouse Professional products
honeywell fob. there are also honeywell compatible available
Id look at the fike twinflex or better the addressable fike as this provides automatic hush in a HMO type environment
Fike CIE-A-400 2 Loop Addressable Fire Alarm Control Panel [540-0001] - £631.41 : | Best Price Promise | Security Warehouse Professional products
I dont know of a manufacturer that supplies boards only. But may be available as a special order. Usually one would replace the whole sounder to keep it looking as new as spossible as this is the detterent
Re the cctv do you have a preffered brand? Agree on the toy town stuff most budget equipment is exactly that.
Alarm system wise again i dont know your expereience or preffered equipment?