Best bet for gas station/grocery store scanners is to get a credit card (or a separate checking account) that you use ONLY for those purchases - make sure it's a very small balance credit card ($500 or less) and pay it off in full every month. I have a separate checking account that has only a couple of hundred at any time and that's the only account I use as a debit card. I can go online and transfer funds from my main account quickly.