Apologies if this has been covered before.
About 5 months ago we were switched from POTS to VOIP landline. I 'knew' at the time that our alarm monitoring would cease to work but was too busy at the time to get the issue sorted. It is an old Paradox system (at least 14 years old). We did have some minor components upgraded 6 years ago when we moved here but it is still quite limited in its capabilities.
As it happened, for the first two months our VOIP landline was effectively unusable (other thread). I suspected the problem may have been caused by the old alarm system still trying to dial out each day. That turned out not to be the case. The problem was at the Vodafone VOIP server end. But to eliminate the alarm as a possibility, I cut the old house internal phone wiring off at the point where it enters the master splitter. I contacted the monitoring company a couple of times about getting our alarm control panel replaced but never got them to respond with an actual quote. Lack of time, plus the thought of the likely cost(!), meant I still have not followed up further so assumed we have been paying the monthly alarm monitoring fee effectively for nothing for the last 5 months; ie. alarm not actually being monitored.
Late () last night when checking our landline usage, I discovered our landline had been making up to 7 calls a day to a local number I didn't recognise - each call exactly 15 seconds long. These started mid-October. I initially thought one of our computers must have been hacked. Given that our old internal wiring link to the outside world had been physically cut, it did not seem plausible that the calls were coming from the alarm system.
However, on discussing with one of my sons, he reminded me that ~1.5 months ago he had shifted the landline base station to a location more remote from our modem. Rather than having the base station directly plugged into the modem, he ran a short cable from the modem to the old VDSL jack nearby, then plugged the base station into one of the old phone jacks elsewhere in the house. Was a bit of a pot shot but the landline worked fine and has ever since. A lot neater than loose wires on the floor (concrete block walls, concrete slab floor, no roof space so near impossible to add internal wiring without extensively cutting into walls etc).
Turns out that action also re-connected the old alarm system to the outside world, except instead of directly connecting to the incoming wire, it is now re-routed through the phone jack on the back of the modem.
I had always 'understood' that the old alarm system was incompatible with VOIP and needed to be replaced by a modern digital version. But (at a more civilized hour) this morning I have confirmed with the alarm monitoring company that the number being dialed is their local dial-in number, AND that our monitoring has been fully functional since mid-October. Their logs show both the daily test call, and alarm setting/un-setting calls coming through correctly.
Perhaps I missed something, but I don't recall seeing anywhere that old alarm systems can (will?) work over VOIP. Just a matter of connecting through the modem rather than directly to the outside line.
All three companies I spoke to regarding a new base station recommended solutions using mobile wireless connections. None indicated that they had solutions that worked over VOIP, let alone mention that all we needed to do was to connect the line from the alarm through the phone jack on the back of the modem. Now glad I didn't get the system replaced. Saved a hefty chunk of cash.