A self contained alarm is arranged to be attached to a door or near a building opening. One version uses a spring loaded switch held open by a door frame, which closes and sounds an audible alarm when the door is opened. A relay with normally open contacts is energized with the alarm to maintain the alarm until a reset switch is opened by a card or key inserted into a mating slot. Another version uses a rotary trip switch which is operated by a line. The line is placed across a building opening to be guarded and closes the rotary switch if the line is disturbed. A second embodiment uses an arm-disarm switch also operated by a card or key inserted into a mating slot to control a second relay. This arm-disarm switch is placed in a second box on the outside of a door to be guarded to permit arming the alarm after the door is closed. Here contacts of the second relay keep the alarm circuit open until the card or key is withdrawn to provide an arm-disarm function.