I use Google Maps on my phone sometimes as the live traffic info. seems pretty reliable. Fixed camera sites are shown as a small red blob on the map, and there's a faint 'bong' as you get near them. Coming back down the M40 recently though I got a spoken announcement: "Warning, mobile speed camera ahead". And a little further on there was indeed a police camera van sitting on a bridge over the motorway. A box to confirm whether the camera was still there or not popped up as we passed (which Mrs BTB responded to). I guess this is a new(ish) feature as I've never seen it before ... potentially quite handy though.