Abstract: The problem of false alarms in a burglar alarm system caused by inadvertent opening of a sensing switch is resolved by providing a burglar alarm system switch with a wire brush contact surface on one switch member of a pair affixed to movable and fixed building parts. The switch parts are so constructed to mate the wire brush as one contact surface in brushing contact with the other switch member contacting surface thereby assuring good contact through any oxidized surface layers. Furthermore, when the switch members are retained in mated closed circuit condition, a significant number of the wire brush members make electric contact to establish the necessary closed conductive path to prevent the burglar alarm from sounding and to maintain it even if slight dimensional changes cause the switch members to move relative to each other.