What would you do if a robber held a gun to your back at an ATM?

There are few options and no way to alert police. That's what prompted Joe Zingher to come up with the "reverse PIN" system.

Call 4 Action reporter Susan Koeppen says the idea is simple: If you're being held up, type your PIN (personal identification number) backward on the keypad.

For example, if your PIN is "1-2-3-4," enter it as "4-3-2-1." A phone call will automatically be made to notify police of your location, without the thief's knowledge. Meanwhile, the machine will distribute the cash so you can hand it over.

"I realized since the only thing the criminal is going to allow me to do is enter a number on a keypad, I would have to make that the way to call for help," Zingher said.

Most banks don't use "reverse PIN."

Jeff Quayle, of the Ohio Bankers League, said banks are serious about protecting customers and their money, but he doesn't think mandating the use of a system to do that is always the best idea.

"It's very difficult for municipalities to provide police officers for safety for their citizens," Quayle said. "To add a system where there could be a high degree of false alarms is going to take away resources where they might be better used."

Zingher, who holds the patent on the "reverse PIN" system, said he will allow banks to use it for free, but no one has taken him up on the offer.