The sensing methods used on the Sandia Hand and the iRobot hands are different, although in general, both methods are attempting to estimate the external force on the skin by observing displacement of the skin material, albeit in different ways.

The Sandia Hand's method uses transflective IR sensors. Each sensor is a closely spaced LED-phototransistor pair. The LED shines through a thin, clear layer of silicone onto a white layer of silicone. As external forces deform the skin, this clear layer of silicone is "squashed" and becomes thinner, resulting in a larger photocurrent, due to the LED light reflecting off a closer surface. The photocurrent is measured and returned as raw 16-bit ADC values.