If you have ever used a biometric lock which scans some part of your physical body to permit access, you may have been reminded of the scanner on your home or work computer, and in fact you are not far wrong.

Access control devices such as fingerprint readers do rely on a scanner, similar to commercial hardware, to collect an image of a fingerprint (or other structure).

Software then compares this input with information within the database to determine whether there is a match. Like the scanning hardware you may have uses, not all scanners are the same quality.

The Difference a Number Makes

The resolution of scanners and similar devices including printers, monitors and even digital cameras is measured in dots per inch or DPI.

This measurement was originally used to determine how many dots per inch a printer could achieve when creating a document. A higher DPI indicated that a printer could produce a document with higher precision; however, this increased the time it took to print the document. Therefore, people would sometimes lower the DPI setting to shorten printing times and reduce ink usage.

With screened devices such as a scanner, DPI technically refers to the pixels per inch which the scanner is capable of reading. As with a printer, higher pixels per inch ratio will produce an image of greater quality than a lower DPI.

This difference is noticeable when the image is enlarged, as with graphics programs. This is requires a longer scanning time.

When you take an image at a lower resolution, the quality may be too low for software to read. This could result in false rejection, even when the input matches an image in the database.

biometric locks could deny your access even if you should be permitted.

Before You Make a Purchase

It is tempting to lean toward biometric systems which have a lower resolution because the actual scan takes less time, especially if you require this device to work frequently and with many permitted users.

Remember that a fingerprint is small and access control devices which measure an entire hand or face can take longer to complete a scan.

Commercial biometric fingerprint locks—the type which you might use for home or small business use—commonly have a DPI of 500 and only take a matter of seconds to scan a fingerprint. A device with a dots per inch ratio of 400 or higher are considered high resolution while systems with a DPI of less than 100 are considered low resolution and may not be as reliable.. Currently, some biometric locks have a resolution of 560 DPI and are considered "state of art."

Of course, when you are shopping for a biometric lock, it is also important to keep in mind the rates of false acceptances (FAR) and rejections (FRR), as well as the database capacity (especially if you plan to program over 100 users into the machine). Vital information such as the DPI resolution, false acceptance rate and false rejection rate will be listed in the product description and you should familiarize yourself with these specifications before making a purchase.