I used eight fingertip sized lasers which I got from Aliexpress, in a bulk order with a bunch of other people a year or two ago. Additionally I used three AA batteries and a plastic battery holder for them, some scrap black leather, a rocker switch, hot glue, and solder. Tools needed were only scissors, a razor blade, a soldering iron, and a sewing machine, although the sewing is minimal and needle and thread would be just fine too. I also used a breadboard for testing the electronics, but you could get away without this and just hold the leads together by hand or with a clip.
Step 1: Test Lasers
Step 2: Prep the Band and the Lasers
Next I marked on the base strip, where each laser would attach. I marked on the laser lead wires where I would solder them together to power them all in parallel. Then I cut the leads at the longer markings and stripped a quarter inch off the ends of each lead, leaving the last set long to attach to the switch and battery.
Step 3: Solder and Glue the Lasers
One at a time, I hot glued each laser onto the band at the X marks I'd made. As I went, I soldered the previous laser's leads to the scrapes on the current laser's leads. Black to black and red to red; lasers are polarized. Once they were all glued and soldered, with the long lead laser last (LLLL for short), I tested again using the breadboard to be sure my soldering was all good.
Then I hot glued over the solders for insulation, placed the leather strip with the holes in it over all the lasers to cover the wiring, and glued that down.
Step 4: Switch and Battery Pack
This switch is actually a lot bigger than necessary, but it is what I had lying around. A small slider switch would have been better, but anything that's not heavy enough to fall off the leather band is fine. Mine had leads attached, which I removed, but most don't. I soldered the battery pack negative lead to one of the switch terminals, and the laser negative lead to the other. It doesn't really matter which is which as all the switch is doing is opening or closing the connection between them. If you have three terminals on your switch, you'll want to choose two by testing. Usually you want the middle terminal and one of the end terminals, leaving the other end terminal unused (if you look closely you can see that my switch actually had space for a third terminal, on one end, but it has been removed).
After this soldering, test again with the batteries, and if all is good, go ahead and hot glue the switch down. Also put hot glue over the solder joins, for electrical insulation.
Finally, attach the strip to a hat! A hard hat would provide excellent support (you might want to use a couple additional lasers), but almost any hat will do. I found that when wearing mine, the lowest laser on my forehead was arranged so that I could aim it at things while wearing the hat. For some reason this was ridiculously fun to do.