Input Devices

A keypad is an example of an input device.  Other examples include a card swipe, prox reader or biometric fingerprint reader.

Input devices are the sentry at the door, allowing access to only those that present proper "ID".

When authorized credentials are presented, the input device signals the power supply to unlock the door.

The keypad shown above is a special high security version.  The circuitry that is the "brains" behind the keypad is housed separately.  This prevents an intruder from tampering with the exposed keypad and defeating the system.  The circuitry is mounted inside the building where an intruder cannot attack the component.

How They Work

Input devices are powered by a single wire leading from the power supply (1).

The power flowing to the input device is always "on", represented by a solid line.

Once a valid code is entered, the input device sends a signal back to the power supply (2). 

This signal only occurs some of the time, so it is represented by a dotted line.

The power supply knows to unlock the door when a signal is received (2).

Device Types

Many types of input devices are available on today's market and the competition has reduced prices while increasing features.

It's important to remember that all types of input devices do the same thing - send a signal.  Technically, a common light switch could be mounted outside the door.  Flip the switch and gain access.

But input devices typically contain complex circuitry, especially when the device is a keypad.  Card swipes and prox readers don't often have extra features beyond simple code acceptance.

The figure above shows a typical keypad circuit configuration.

Input Device Tips

Here's a few pointers to get you headed in the right direction.

Quick Tip

Keypads offer more features than card swipes or prox readers.

Quick Tip

You can mix and match input devices.  A system initially installed using a card reader can swap out a keypad in its place.

Quick Tip

To select a keypad, start with the number of user codes it will hold.  Will you need 50 codes, 100, or more?  Next, determine what additional features you require.  Common features include: anti-tamper protection, panic button, silent alarm code, etc.