That's even easier. Just make a resonant circuit, and do some antenna design.
But, to what use are you going to put it? Is it more cost-effective to build your own? Are you going to 'hack' someone else's ID and answer for them?
----- "Matt Guthrie" <stampeder@xxxxxxxxx> wrote:
> I don't know what was used before the iclickers, but the current
>
> system is RF based.