I use and reccomend the Valentine 1 (from USA)

OK, it's a bit "low tech" compared to modern rivals BUT it is the most sensitive device for advance warning of fixed camera sites (radar).........also, the lazer detector is good but of course it can be too late to react to "instant on" laser gun/camera once you've been targeted

http://www.valentine1.com/

Not tried the S4......but heard that it is VERY good