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Ab RFID Security System

Here's a high-security system that's very easy to build but offers you peace-of-mind for your home, car - in fact, anything where entry needs allow the good guys in but reject the bad guys. Team it with an electric lock and you can have a keyless entry system as well!

By Jeff Monegal

It’s a sad fact that in today’s world the need for property security is ever present. Our homes and business properties are a target for thieves and other criminals.

We spend countless amounts of money on systems that have been designed to counter the would-be bad guys.

The complexity of these systems ranges from a simple sticker that proclaims Batman will jump through the window and zap any burglar stupid enough to attempt robbing the premises, all the way up to computer controlled alarms systems that use satellites to protect our property and warn of a crime in progress.

Although the system presented here does not quite communicate with satellites it will give a high level of protection and control access to any structure that it is monitoring.


If you have an E-tag for the tollway, a micro-chipped pet or a late-model car with an immobiliser key, then you’re already using radio frequency identification (RFID) technology. Although RFID is not a new field and it has been written about in this magazine in the past, it is now available as a project for any person who wants to protect their property from unauthorised access.

Click for larger image
The project is very easy to build – all the hard parts (the RFID module and the detection coil) are prebuilt, which leaves you with only a handful of components to solder onto the PC board. The relay output can switch an electric door strike, a car central locking system, another alarm or just about anything you want!

This system will give control over who has access to your home, car or any other building you care to mention. The system is installed in a position that will allow the users access to the protected building.

A tiny (keyring-sized) RFID tag is held close to the sensor. The system detects the tag and compares its “signature” with those stored in memory (up to eight).

If, and only if, a match is found, an on-board relay is enabled for one second. This relay could be used to disarm a burglar alarm or unlock a door.

If the detected tag is not one of those stored in memory then the system can be used to trigger an alarm or to sound a warning that an unauthorised access has been attempted.

Click for larger image
The “works” of the RFID tag is tiny, as this photo shows. Very close to actual size, this is the same tag that's encased on the keyring shown above left.

The advantage of this is that tags can be changed and the system re-programmed at will, so if a tag is stolen or even if someone attempts entry who is no longer allowed, that tag will have no effect except to flag an unauthorised entry attempt.

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