Concealed alarms

1931. The concealed alarm is a system of wires spread over a garden or orchard, like those of the spring-gun, and terminating in a bell or gong alarm, which goes off when any of the wires are disturbed. This alarm may be in or near to the gardener's room, watchtower, or other suitable place, though at a considerable distance from the wires. This is, perhaps, on the whole, the best way of detecting intruders. In addition to setting off an alarm, the same wire may let loose a watchdog, drop a heavy body, or a fulminating glass bead, discharge a gun, &c.