If you can't do that or you have no good idea: don't do it. There is no pressure on anyone to deliver a "badge" at a hacker event. It is a non-tradition.
Also: where is the creativity here? Hacker scenes find themselves to be super-creative (and they are) but often they fail to think from the user to the device not vice versa.
If you start with technology you will end up with technology. but there is no value in it itself.
Instead start with a problem and then solve it.