Lancets are small needle-like medical supplies. With a lancet, you can make a tiny prick in your skin to obtain a few drops of blood for testing in a diabetic monitor. Lancing devices are used with lancets. Most have a spring action that allows the lancet to move quickly enough to pierce the skin. While lancing devices, themselves, are reusable, it is important to use a new lancet each time you check your blood sugar to help prevent infection.