Door Protector
Approx construction cost US$16
The first in a series of "Top Tenner" projects, featuring simple designs that can be built for around 10 UK pounds (16 US dollars).
Even if you already have an electronic security system installed in your home or workplace, there is likely to be a use for this Door Protector. With any security system, or even with none, it is important that all doors and windows should be protected by bolts, bars, grids, or other physical means. It costs relatively little to fix strong bolts or locks to windows and doors, to make it virtually impossible for anyone to gain access without employing drastic measures.
Unfortunately, there is nearly always one weak point. This is the Exit Door, the door by which you normally leave the house when you are going out. This is also the door by which you enter the house when you come back home.
Other doors (and the windows) are bolted or locked from the inside. Once secured, they can only be opened by someone who is already inside the house. Only physical protection is needed. By comparison, the Exit/Entry Door has to be openable from outside the house as well. There is a limit to the number of locks that can be fitted, and usually it is not practicable to fit any bolts.
This is where electronics, in the form of this month’s project, can be of help. The Door Protector system described here can be set to one of two states:
Disarmed: After pressing the Disarm button, you may open and close the Exit/Entry Door as often as you like and this has no effect on the siren.
Armed: You arm the system by pressing the Arm button and then have 20 seconds to leave the house via the Exit Door without making the siren sound. On re-entering the house through the same door, nothing happens for the first 20 seconds but your entry has triggered the system and the siren will start to sound after 20 seconds unless you press the Disarm button.
The timings can be altered to suit individual locations. Of course, the function buttons are hidden away so that an intruder cannot quickly find them.
More details on this construction project can be found in the August 2000 issue of EPE Online, the world's first web-delivered electronics and computing hobbyist magazine.
PURCHASE this issue or peruse more Projects