I have just moved in and property has this alarm. We turned off the mains electricity which was fine but when we turned it on again the alarm and bell came on. Tried to reset to factory settings by disconnecting mains supply to alarm, disconnecting battery and then reconnecting and putting code in but alarm goes off as soon as mains connected. I have disconnected mains supply to alarm so it’s all quiet but worried alarm will start again later. 

When was it last serviced. Id assume the battery is failed. If it had no power to it it probably has at least 1 fault on it. You will need to find and fix the fault/faults.

Also an xm will not default when removing the power so if you dont know the code it wont reset anyway

With it completely powered down, mains and battery with no sounders ringing then it should be fine.

If you want it working I suggest you find someone come out and recommission/service it for you.

Expect for some things to require replacement like the standby battery and possibly the bellbox from what you have said.

On 06/09/2020 at 18:33, Terry S said:

I have just moved in and property has this alarm. We turned off the mains electricity which was fine but when we turned it on again the alarm and bell came on. Tried to reset to factory settings by disconnecting mains supply to alarm, disconnecting battery and then reconnecting and putting code in but alarm goes off as soon as mains connected. I have disconnected mains supply to alarm so it’s all quiet but worried alarm will start again later. 

Optima panels while limited are very good reliable panels    if you don't know the code have a company default the panel