A system for monitoring frost on a windscreen of a parked vehicle includes temperature sensors, moisture sensors, optical transmission measuring etc. to determine the degree of frosting. The system includes a telemetry link to a remote receiver, e.g. beside alarm clock to provide a warning of frost and/or to advance the alarm clock enabling the owner to rise earlier and have extra time to clear the windscreen. The telemetry is via em radiation, e.g. radio, IR etc. The system includes a manual override.