A security system for a boundary is generally shown as (1) in FIG. 1. The components comprise an elongate member (2) and a support (3) for the bar. The bar support (3) can be fitted to boundary support. A conduit (7) extends through the housing (3). The rod is surrounded by a resilient member. The boundary supports (4) and the bars (2) are in communication with a circuit monitor unit (17) and from an electromechanical disturbance mechanism (EMDM) unit for detecting security breakdown of the boundary.