A lock monitoring device includes a detection unit and a plurality of sensors, where the detection unit is configured with a thin circuit board configured with a plurality of detection elements, allowing the detection elements to be connected in parallel with a circuit and then connected to a control circuit; the sensors are configured on parts of the lock such as lock tongues, rotating shaft and correspond to the detection elements; whereby, when the lock is unlocked and locked, the detection elements will detect that the detection elements depart from detection positions and send detection signals to a remote monitoring host, and the monitoring host monitors and records the number and time of the unlocking of the lock, achieving smart access control and further allowing the lock to be safer.