I really like the Petzl headlamps, which now have a natty push button switch on the top.
They used to have a tiny, stiff sliding switch which made it really difficult to turn one on in the dark. You could spend quite a while forcing the slider in the wrong direction (because it was stiff even in the right direction).
Today’s invention is a simple way for lamps like this to preserve the old switch design but to ensure no more delays when the light needs to be lit.
It consists of a foolproof way to orientate the lamp, even in the dark and when working with one hand. A pair of closed-ended tubes would be moulded into the body of the lamp (or retrofitted in the form of a collar). These would be simple to locate by touch alone and correctly orientate the device for either left or right handers.
The user would know that these should accommodate index and second fingers, allowing the thumb infallibly to push the switch on, opposed by the fingers gripping the tubes’ interiors.