The number of sensors you need will depend on the size of your home. Most alarm systems feature 2-4 passive infrared sensors (PIRs) for motion detection, and 2-4 magnetic contact sensors on doors and windows. An alarm company will advise you of how many your property will need upon an inspecton.
Lifton
Lifton is a town and also civil parish in Devon, South West England near the assemblage of the rivers Wolf and Lyd, 1 1/4 miles south of the A30 trunk road and very near the border between Devon and Cornwall. The town becomes part of the electoral ward of Thrushel. The population of the surrounding Thrushel ward (that includes the town of Thrushelton to the eastern of Lifton) at the 2011 census was 1680. The village was bypassed by the A30 in 1993, and today, abnormally for such a little area, Lifton is a post community as well as has a number of young people football teams. It also has the 1st Lifton Sea Scouts.