ID Scanners are available at various price points. Before purchasing the least expensive Drivers License Scanner, one should understand that not all are created equal. The less expensive units typically read only a magnetic stripe, simply display the cardholder's age and store no information. While these seem like a good deal, they really are not.
First, you need an ID Scanner to calculate age AND WARN when underage for alcohol and often tobacco. Simply displaying the age gives some inattentive clerks the chance serving a minor. A unit that displays age, alcohol/tabacco status and warns when underage is worth the investment when considering the costs of a clerk making a mistake.
Second, you need an ID Scanner to record the transaction to prove due diligence. The less expensive units have no memory or transaction log. You need the memory to prove an ID was checked. Lets say a minor uses their older brother's ID to purchase beer and then when the police investigate, the minor says he presented his real ID which says he's underage. With transaction memory, a merchant can prove the older brother's ID was checked and since siblings look similar, would be able to claim an affirmative defense. Without the memory, the merchant has no proof of due diligence and would be convicted of the infraction.
So before you purchase simply on price, call an ID Scanner company and ask them to compare products.