A radar-based fill level measurement device having a signal generator for the purpose of generating electromagnetic waves, and an antenna for the purpose of emitting the electromagnetic waves into a container, as well as for the purpose of receiving electromagnetic waves reflected out of the container, having a security device for the purpose of verifying the functional capability or improving the measurement quality of the radar-based fill level measurement device, wherein the security device has a reflector and an adjusting device, and is suitably designed to move the reflector between at least a first position, in which it reflects the electromagnetic waves, and a second position, in which it reflects the electromagnetic waves to a reduced degree, and wherein the security device has a drive which acts on the adjusting device.