Police say it 'beggars belief' that people leave their car keys in their vehicles.
They were speaking after two cars were stolen from Ramsey last night.
One, a red Ford Escort, went out of control and overturned on its side near the Gooseneck, before the driver was seen running away from the scene.
The other, a red Volkswagen Golf with the registration number EMN 444F, is yet to be found.
Inspector Derek Flint from the Northern Neighbourhood Policing Team can't believe the important message in the recent Operation Key Snatch has been ignored.
He told Manx Radio:
"We are appealing for the public help to try and trace that car (the Golf), so we can maximise any forensic opportunities.
'The frustrating thing with this is that despite all the activity we did with Operation Key Snatch, trying to ram home to people the importance of taking their keys in at night, these cars were both taken because the owners had left the keys in them.
"Now, I don't know whether it's going to take an abject tragedy - a bus queue being taken out or somebody's loved ones being hit by a stolen car coming the other way - to bring the public message home!
"Take your keys in at night and secure your cars [because] there are people out there who can't resist temptation."