An underrated extension cord is a fire hazard.

Yes. If the cord can’t handle the power draw, it heats up. Enough heat and you get a fire.

You don’t need an engineering degree to check. Look at the device’s label—it’ll say watts or amps. (If watts, divide by 120 to get amps—assuming US standard voltage.) Then check the cord’s rating: it’s printed on the cord or packaging. Match or exceed.

A cheap 16-gauge cord might be fine for a lamp but not a space heater or saw. A space heater can pull 12-15 amps. That needs at least a 14-gauge cord, preferably 12-gauge. Don’t guess.

If you’re unsure, buy a heavy-duty cord rated for 15 amps or more. They’re not expensive. The alternative is watching your garage burn down because you saved eight bucks.