For finding needles in haystacks

It's always annoying when you loose a screwdriver bit ('bit' here meaning the little interchangeable points), today I knew it had flown into our only bit of long green grass..... but I also knew that (ever since an impulse buy from the middle aisles in Lidl) I had the technology to find it! The red thing is a welders clamp made up of two incredibly powerful magnets, the only problem with it is trying to keep it clean of all the iron filings and bits of steel rubbish that it invariably manages to find.