Britney's two boys are safe and were handed over to Kevin Federline around 11:00PM.
According to TMZ, when cops arrived at the scene, they said that Spears was "under the influence of an unknown substance."
The ambulance is still in her driveway, but is ready to take off!
UPDATE: Britney was just wheeled out of her home and into the waiting ambulance. She is being taken to a hospital on a "medical hold" and a mental evaluation.