An elevator monitoring device has a safety chain, an I/O device, and an interface device. It is to be possible for safety signals from the safety chain to be relayed to the I/O device and passed on therefrom, for example, to an external control device. In order to prevent transmission of, for example, dangerously high electrical voltages coming from the safety chain, the interface device is connected between the safety chain and the I/O device. The interface unit contains a signal transmission device that is designed to relay galvanically decoupled signals from inputs to outputs. This makes it possible for safety signals to be read out from the safety chain with the highest possible degree of safety while avoiding electrical overvoltages, and for the signals to be provided to the control device.