Like most people I don’t have a dedicated workshop, meaning my power tools share the garage with lots of things that aren’t happy about sawdust wafting over them like the morning dew. The solution is a Shopvac, but it can be a real hassle remembering to turn it on/off as I turn on/off my table saw, hand sander, Ridgid Oscillating Belt & Spindle Sander, etc. I’ve been woodworking at home for perhaps 18 years, and the best solution I’ve found is one of these little outlet boxes, which powers up multiple tools automatically.
You simply plug your main tool into the top outlets, then plug your vacuum or work light into one of the other two accessory outlets. Whenever you turn your tool on, it will automatically turn the other outlets on. When you turn your tool off, it waits a few seconds before turning the accessory outlets off, which is useful for clearing the line of dust, etc. I have two in my shop — one for each Shop-Vac so I never have to reconnect power cords or vacuum hoses!
I’ve been using these switches for four years. They definitely save time. On a given woodworking project, I generally turn machines on and off every few minutes and move from machine to machine. Without this switch, you would spend an extra 3 seconds and 2 steps turning it on and another 3 seconds and 2 steps turning it off. Doesn’t sound like much, but in reality those seconds and steps really start to add up, so you’d just end up leaving the vacuum on or using some other less effective dust collection (for example, an on-tool dust collection bag).
I had a discussion with someone about 9 or 10 years ago about how you could build one – and I actually found schematics for a load sensing relay that you could make one with. But for $20, this switch certainly beats trying to round up the components and DIY.