A modular intrusion detection system that includes a base unit having a
primary intrusion detection device and a housing. The primary housing
includes a base housing section and an outer cover. The base housing
section includes a first mounting interface. A plurality of different
secondary housing sections having a second mounting interface which can
be attached to the first mounting interface of the base housing section
are provided. The secondary housing sections may have a functional
device, such as a CCD camera or a microphone, associated therewith. The
camera or microphone may be activated to an alarm signal generated by the
intrusion detection device. A plurality of different base units, each
having an intrusion detection device, may also be provided wherein each
of the base units is attachable to each of the secondary housings, and
secondary devices associated therewith, to provide flexibility in
assembling individual devices.