About three years ago I took a Britannia flight from Manchester to Sanford. As we taxied towards our gate you could here numerous seatbelts being unfastened. The captain came on the intercom and said that he had a newly installed 'seatbelt detector' and that he would stop the aircraft unless everyone fastened their seatbelts. Slowly but surely you could here all the seatbelts being refastened. I thought it was quite amusing at the time !!