Mine is the same if your car is old 2000 ect, it is very likely it's the "Airbag Rotary Switch" located in the steering. This will have to be replaced but the part is costly, not sure how much but over £100 (I work for Peugeot...staff price £98.99) You might look for one at a salvage yard or parts supplier.
If the car's a little younger then you probably don't have this switch, in that case it can be the wire that runs close to the mechanism that moves the drivers seat back and forth. You may have found that that's what triggered it before! Then it needs tightening. If you know someone good with cars they could fix it for you.
Hope that's some help :)
Mandy
November 2013