Police have searched a farm in Sixmilecross, County Tyrone, over fears a bomb may have been attached to a magnet found under a tractor.
The magnet was found when the farmer, a former member of the security forces, left his tractor in for servicing.
Police retraced the route the tractor had taken over the weekend - searching fields and roads - but found nothing.
Booby-trap bombs have been found under the vehicles of three security force members in the last week.
Those incidents happened in Bangor, Kilkeel and Cookstown.