When operating any kind of power tool it’s important to know where your fingers are, at all times. Monitoring this is a surprisingly demanding mental task, especially when concentrating on actually doing the work.
Today’s invention attempts to ensure that one’s fingers stay safely attached.
Any given tool would have two runners permanently attached so that the edges of four rings would fit into each (think shower curtain rings here). These rings would be slightly sprung apart from one another. To start the device in question, press the ‘on’ button as usual, insert four fingers from one hand into each bank of four rings and squeeze the rings into contact with each other. This would form a circuit, powering up the device in question.
In this way, only when one’s fingers are correctly located and the tool held firmly will it operate, thus ensuring that you can’t run the motormower/ chainsaw/ router etc when fiddling with the spinning sharp bits.