The Builders Hammer

Electrodes powered by your skin are networked to your phone that calculates everything using the sensors in the hammer, which means if the axe or hammer is ever swinging towards you or anyone else networked to the app, it would automatically stop, by tracking those small electrodes that just need to be pinged so they can be powered by the skin electricity generator, easily put a few all over your body, and you wouldn’t notice them after a few hours.