Capacitive sensors work from a process known as capacitive coupling. Capacitive sensing technology can detect anything that is conductive that comes into contact with it. One of the most commonly used forms of capacitive sensing is with devices that work by detecting changes to their surface capacitance, although projected capacitance can also feature in some product designs, too. With surface capacitance, capacitive sensors detect some form of contact, such as a human finger. This sort of technology is often used in things like tablets, smart phones and other human machine interface devices which utilise touchscreens. In other cases, a stylus or similar object can create the change in capacitance that these sensors detect. A good number of this capacitive sensors use different types of capacitive sensing, such as proximity sensors which both detect and measure the closeness of another object. Others might detect things like displacement, humidity or acceleration. Sensors with the ability to detect electrical capacitance are made from a variety of materials which include copper, printed ink and, in some cases, indium tin oxide.