The most popular devices available for protecting paintings and freestanding pedestals are (1) light beams focused along and parallel to the wall, (2) magnetic contact switches attached to the painting frame, (3) mercury switches that are activated if tilted, (4) capacitance protection that senses human movement near the surface of the painting, (5) shock sensors on display-case glass, and (6) buttons mounted beneath a pedestal. Two new wireless techniques that are more effective than the normal hard-wire systems are a wireless transmitter attached to a shock sensor and an ultrasonic transmitter mounted on the ceiling with ultrasonic receivers mounted inside the display case. A new set of devices, calling volumetric alarm systems, has been developed to cover a museum perimeter and critical interior areas. The term 'volumetric' indicates a flooding of an area with unseen 'waves' that detect movement throughout the space. The most accepted techniques are ultrasonic/ultrasound, microwave, audio, and passive infrared. Due to the peculiar configuration of most museums, care must be exercised in the selection of one intrusion device over another. The detectors selected must be able to flood areas. The most effective system is to align the detectors in a checkerboard pattern so that a criss-cross effect is achieved in the area to be protected. The selection of a reliable system to transmit the alarm signal is just as important as the selection of the sensor. A silent alarm transmitted to a location outside the facility is generally superior to most local alarms. The primary communications/transmission systems are tape dialers, digital communicators, McCulloh loop and multiplexing networks, dedicated/leased direct wire phone lines, and radio transmission (FM).