Franzis 65293 alarm system kit franzis 9783645652933 p the franzis alarm system kit detects intruders by measuring the slight variation in air pressure caused by opening doors and windows this is called volumetric sensing and has been used extensively in car alarms not to be confused with the vibration alarms that are also used this type of sensing means there are no wires to route around your house or office just place the alarm and switch it on you can adjust the sensitivity to moni