This alarm employs only three components: a set of batteries, a relay and a pressure switch which can be either a bell button or a pair of blades. Another possibility is to use a microswitch.
As we can see by the circuit, the switch can be adapted between two hinged boards and placed under a tape or entrance mat of a store or residence. When someone steps on the mat or rug the relay closes its contacts and locks, triggering an alarm. To disconnect, simply remove one of the batteries for a moment. In Figure 1, we have the diagram and assembly of the alarm.
The relay is 6 V with coil current up to 100 mA and contacts up to 2 A or more depending on what you want to control, batteries may be small, since the consumption is zero in the standby condition.
