Having already modified a Dremel to be voice-controlled, a different nice modification would be to be able to control the Dremel using a foot pedal.

Most Dremels for hobbyists are supposed to be mounted on a vertical pole, above the work desk and the flexi shaft is used to carve or make small adjustments. Unfortunately, the flexi shaft has a major shortcoming: it cannot control the Dremel, so, in most cases, one would have to stand up and flick the on off switch. This is very inconvenient when working since frequent stops or breaks are necessary even for the brashest of jobs.

The schematic is very easy to comprehend, it consists in severing the power lead of the Dremel and then placing the foot pedal such that it interrupts one of the wires:

+--------------+
|    Dremel    +--------------------------------------------------->
|              +---------------------+ +---------------------------> Wall Socket
+--------------+                     | |
                                     | |
                                   +-+-+-+
                                   |     | Foot pedal
                                   +-----+

Most foot pedals are just a momentary single pole dual throw (SPDT) switch that will close the circuit once the pedal is pressed.

Alternatively, a foot pedal with a locking mechanism would allow the user to activate the lock and work without having to hold the pedal down to make the Dremel turn.

Following the voice controlled Dremel tutorial, the result can be combined such that the Dremel can be activated both by voice and by a foot pedal.

In this case, the connection is made in parallel to the Sonoff such that both circuits can switch.