When you install the website tracking code on your landing page(s) ClickGUARD is able to track visitors' devices (browsers).
ClickGUARD uses browser local storage to store a Device ID that is used to track visitors cross multiple ad clicks, campaigns, keywords, etc. You can later use this information to detect repetitive ad clicks from the same browser (device).
With ClickGUARD you can define No Device rules that trigger when ClickGUARD is unable to track a visitor's device after an ad click, as well as use "device" as source in almost any other rule type to focus the rule on unique devices. You may also deal with "no device" clicks with Simple Visitor Behavior rules.