I recently found my ForFour tyre pressure indicator warning light had come on. checked all four tyres, and they were all 10psi lower than the indicated on the drivers door frame. Now I would suggest that this indicates that the car was delivered with low pressure on all four tyres, as for all four tyres to have lost 10psi is highly unlikely. Pumped the tyres up to the recommended 32psi front, 36psi rear and the ride was much quieter and less bumpy. So if you have recently purchased your Smart, checked the tyre pressure.
As the temperature drops, expect it to play havoc with the pressure sensors - especially if there’s a sudden drop in temperature overnight and/or you keep it garaged.
had the same thing on my ED , the tyre sensor system isn’t too smart and allows the alarm to be set with different values of all tyres.
Had a similar issue after receiving the car back from a service. The tyre in question didn’t seem less inflated than the others, but they were all quite low. After pumping tyres up about 15psi more than they were I’ve not had the issue since.