An elevator safety device 16 for monitoring a landing door 10 of an elevator system 2. The elevator system 2 includes a landing door sensor 14 arranged to detect a state of the landing door 10. The elevator safety device 16 includes a power source 20 arranged to power the landing door sensor 14 independently of a power supply 19 of the elevator system 2 and a memory 22 arranged to record a state of the landing door 10 detected by the landing door sensor 14 when the landing door sensor 14 is powered by the power source 20.