Abstract: A motion sensing circuit has a plurality of motion sensitive switches connected serially therein and which conduct a quiescent current through the circuit in one stable condition whereas in another stable condition of said switch above a upper limit of the tripping, the quiescent current flow is re-established and, in between the current through the switch is interrupted. In both stable conditions the switch represents a short circuit, that is current flows through the circuit, while between the two stable conditions the current is interrupted and a registering device at the output of the circuit will sense such tripped or alarm condition.The switches according to the present invention employ mercury as the moving contact and a pair of rotational body-shaped rest contacts within the tripping sensitive switch. The rotational body-like shaping of the motion sensing switch causes the mercury to flow from one stable condition into the other during the tripping quickly.