In my country the line detection doesn't exist but alarms do have backup batteries. I have known cases in my area of houses that got broken into with the use of

In my country the line detection doesn't exist but alarms do have backup batteries. I have known cases in my area of houses that got broken into with the use of a GSM jammer. Especially if a household relies on broadband telephony, knocking out the land line is a matter of turning the power off.