They can reveal the location of every enemy zombie within their radius. Their zombie counterpart is the Superb Zomboss Radar. They can be destroyed by the zombies. They take 20 seconds to recharge.
Nothing tracks illicit Zombie activities better than a Coconut Spotting Station. Place them around the map to flag the Zombie location for your team.
Plants vs. Zombies Wiki has a gallery for Coconut Spotting Station.