From their site: “Generates a unique six-digit security code about every 30 seconds. You enter that code when you log in to your PayPal or eBay account with your regular user name and password. Then the code expires – no one else can use it.”
Cost: The PayPal Security Key is available for a special introductory fee of $5.00 USD. (The fee is non-refundable.) If your Security Key is lost or damaged, you can order a replacement for the same fee.