Path: utzoo!attcan!uunet!zaphod.mps.ohio-state.edu!sdd.hp.com!hp-col!hpldola!hp-lsd!davem
From: davem@hp-lsd.COS.HP.COM (Dave K. Martin)
Newsgroups: sci.electronics
Subject: Re: Ideas needed for Car Alarm Arm/Disarm method
Message-ID: <25150015@hp-lsd.COS.HP.COM>
Date: 26 Mar 91 19:35:34 GMT
References: <17748@sdcc6.ucsd.edu>
Organization: HP Logic Systems Division - Col
Lines: 15

Wayyyy back when, I recall having seen a Popular Electronics article on a key-
less lock.  It was in the early 70's I think but am not sure.

Anyway, the article described a small oscillator and a receiver mounted on a 
small board.  The 'key' was a small plastic cube with a pickup coil and an
oscillator.  The pickup coil would pick up enough RF to power the osillator 
in the 'key'.  When the receiver picked up the apropriate frequency (and 
probably modulation), it would toggle the state of the output.
To unlock, the key just has to be held close (2-3 inches?) from the transmitter
receiver pair. 

All in all, a pretty elegant little design.  Virtually pickproof and no
batteries in the remote to worry about.  I may still have the P-E issue 
somewhere.  If you want to follow up on this approach, email me and I'll see 
if I can find it.