An apparatus and system for sensing vibration in rotary or reciprocating machinery, such as motors, pumps, fans, gearboxes, compressors, turbo-machinery or high-speed spindles, which comprises a mechanical isolation member (14) interposed between a sensor base (15) and a main sensor body (11). In one aspect, the mechanical isolation member comprises a coaxial cylinder of plastic, rubber or polyurethane which is compressed between the sensor base and main sensor body.