Hi - I use a radar/laser detector which (as noted above) bleeps a lot through towns and when passing petrol stations etc. It bleeps madly if a gun is pointing at you (which happened to me but by then it's too late!) but in a perfect world hopes to give you a warning of laser 'splatter' going on up the road ahead. It's clever and an intersting gadget, but if I lost it tomorrow I don't think I'd bother replacing.
I would however definately recommend a speed camera warning system and recommend getting a dedicated unit rather than a TomTom type sat-nav warning. With most sat navs you pay a subscription for cameras every year and of course the system only works with your sat nav switched on - navigating you. When not being navigated you have no camera warning.
I use the Novus Piccolo, a cheap unit costing just £59 to buy outright and gives you free camera database updates for life. At that price it soon pays for itself compared to yearly sat-nav subscriptions, plus you have the peace-of-mind "always on" dedicated unit.
Hope this helps. See a video of this tiny thing in action...
http://www.novus-gps.co.uk/Novus_piccolo.php