This paper proposes for the first time an optical touch switch based on total internal reflection (TIR). Key features include ease of implementation, prevention of the light beam from becoming incident directly on the user's eyes, and ability to accept both strong and weak mechanical forces from users. Experimental proof of the concept in the touch-off, release-on mode using a Dove prism shows that a small electrical load (e.g., an LED) in the on state can be turned to the off state by just placing a finger with a measured small force of 0.3 N. The optical loss of 0.4 dB is also measured; it is due to back reflection from the Dove prism. In addition, two methods for removing the finger from the touching surface are studied, indicating that slide-out is suitable in practice for operating the TIR-based optical touch switch. © 2003 Society of Photo-Optical Instrumentation Engineers.