The way the gas pumps work is if you don't insert a credit card, and you take the pump out to pump gas, it will ring an alarm on the register and ask if you want to approve the pump or not. That is, if it's not a pre-pay only pump. Around here, which is a bit further up north and a little more rural, the only pumps that are usually prepay are the ones farthest away from the building. So, if the 911 caller got there, and picked up the pump it would just keep saying "please wait" or whatever it's programmed to say, and the register would just keep making the sound over and over. It's a sound every gas station employee could recognize in their sleep, probably, since almost every gas station I've ever seen uses a RUBY system.