The Fluidmaster 400LSR Leak Sentry Universal Fill Valve includes a water saving roller clamp to make sure that the right amount of water goes into the bowl with every flush. It’s also the only toilet fill valve with active leak detection, preventing a toilet from leaking without the homeowner having to take any special action. Best of all, when there’s no leak in the tank, it works just like a 400A toilet fill valve, so you know you’ll get consistent performance flush after flush. Automatic “Locking” action alerts users to leaks before money and water are wasted. Toilet remains fully operational, easily resets with touch of tank lever. Anti-siphon, code approved.