Better yet... raffle off a prize, that requires names, addresses, and phone numbers on the tickets.

This will garner more contact information, but the prize has to be carefully selected, so that it generates high amounts of interest, but (hopefully) only from people that may be potential clients.

Items that seem more expensive than they are, and require installation (but nothing too difficult), are good candidates -- alarms, satellites, in-wall speakers, etc.

A Pronto or equivalent would be great too, but you would have to stress that programming is included (requiring a site visit), to qualify customers.

Many manufacturers or distributors will co-op or donate equipment, or provide loaners for the show. If you don't sell alarms, you could probably get an alarm company to do the installation for free, so they can get the monitoring contract.

There are many possibilities...