I know a guy here who sells these systems where you call a number, and it allows the gate to open, if your on the list, or if you key in the secret number. So the "key" doesn't cost anything. Its worth it for a small cellular company to do this.

Sell millions of tiny devices installed in doors, that get their electricity from the doorknob, and when called by the cellular phone give the status as busy (for locked) or OK (for open).

Or pay for the lowest rate of call to check, and a true answer will be given. Or best: have an SMS sent to you telling you the answer.

People would put this in their front doors and in their car doors, and in the garage doors, and even in pad-locks for gates etc.

This is an implementation of the Lock indicator ideas of Hippo et al.
-- pashute, Jun 02 2010

//that get their electricity from the doorknob//

How?
-- Wrongfellow, Jun 02 2010


built with www.microchip.com that uses pico-watts.
-- pashute, Jun 02 2010


If not from the doorknob from current from the grid.
-- rcarty, Jun 02 2010


"//that get their electricity from the doorknob//

How?"
First you rub your socked feet across the carpet...
-- phoenix, Jun 02 2010


Actually .....

Put an RFID transponder in the doorknob that only goes active when the door is locked.

Then mount the detector unit on the doorframe, attached to mains power and incorporating a cellular modem.

The detector pings the doorknob chip, and reports the status.

Easily Bakeable, but not cheap in small quantities.
-- 8th of 7, Jun 02 2010


When we all move into the House of the Future, this will be a standard feature.
-- swimswim, Jun 02 2010


No, it won't. Our Cube doesn't have internal doors.
-- 8th of 7, Jun 02 2010


Car remote control fob innards- only sends signal when status changes - encoded - battery lasts several years - local, central receiving unit built in simple mobile telephone with SMS facility and permanent power supply with battery back-up...
-- Ling, Jun 02 2010


[+] could be one of the many things a landline can do for you.
-- FlyingToaster, Jun 02 2010


bigsleep, first you have to steal my cellphone. When I install it, I give it a list of phones that I can call from. And after you stole my phone, you only know if the door is unlocked.
-- pashute, Jun 07 2010



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