SECURITY SYSTEMS BROOKLYN, New York

Holding a small fob or token up against the reader plate will send an electric impulse to the door lock to release. The fob readers can be tailored so that the door would release simply by sensing the presence of the fob your pocket or handbag. A fob-reader works in conjunction with an electronic door release or an electronically operated lock. This solution usually looks nice and is suitable for heavy traffic.

4) Biometric readers New York:

The only commercially widely available form is the fingerprint reader. Upon installation the prints of 1 or 2 fingers per user are programmed into the reader. Presenting the correct fingertip to the reader plate will send an electric impulse to the door lock to open up. A biometric reader works in conjunction with an electronic door release or an electronically operated lock. This solution usually looks nice and is suitable for heavy traffic. 
The headway this product makes is slow, mainly because solutions 1, 2 and 3 work quite satisfactorily.

Intercom systems are a ubiquitous feature of both residential and commercial premises. If you need to know who is knocking on your door, then an intercom system is a must.
Depending on the end-user's requirements, intercom systems can be large versions for many users:

This is a flush-mounted intercom system, where the main part of the equipment is sunk into the wall.

Or they can be small, single-user units:
In this case, the entire unit would be fitted onto the wall - this is a surface-mounted intercom system.