How long of a water leak sensor should I get for our network closets?

I've just been tasked with deploying water leak sensors in my company's network closets to help warn us of any impending water damage. Luckily (knock on wood), I've never had to deal with water damage like that before, so I wanted to hear some of your experiences. I think I want to get ones with sensing cables that alert you if any part touches water, but I'm wondering how long the cables should be. If you've used water sensors before, what cable length has worked well for you in the past? Where did you run the cables in relation to your network racks? Thanks!