Does anyone know of a security video doorbell ?

Im looking not only for the typical one in which you decide to let people inside, but also to decide when you let people out. I work with kids, and I dont want them to run off to the streets while Im attending another patient. Thx!
Im looking not only for the typical one in which you decide to let people inside, but also to decide when you let people out. I work with kids, and I dont want them to run off to the streets while Im attending another patient. Thx!

@Vijay:
Of course I want to let them out, but until their parents pick them up, not any stranger!