"Excuse my ignorance, but what does one do with one of these?". Its a security device. The first time you use it you place your finger onto the pad and it will learn your fingerprint make up. Anytime afterwards you may set it to say..not open a certain document, turn on or shut down without your permission..you would need to place your finger on the pad to do so. It would not work if some random person walked by and put their finger on the pad..it has to be yours. Its a nice security device but it can be broken into rather easily. I hope this helps with your question. Also I saw a 3 1/2 inch version while searching yahoo shopping a few weeks ago. you may want to take a look at the yahoo shopping section.