OK, here's one of my favorites..
Shown with a penny for scale.
This is a cheap ($10) pocket-sized Infra Red Thermometer. This one came from Harbor Freight.
This has become an indispensable tool in my self-education into the realities of thermal energy (AKA: "heat").
You just point it at something you want to know the temperature of, and read the temp from the display. It has no laser beam... it's pretty simple.
The angle of acceptance is about 30 degrees, so you have to imagine a funnel of 30 degrees when you read. If you want to read a small area, you get close, a bigger area, get further away.
The beauty of this thing is that it is so cheap and small that it invites you to carry it around in your pocket on a regular basis. On a hot day, point it at the grass... then point it at the pavement. That's a lesson in the efffect of civilization. Then, on the same hot day, point it straight up at an open sky... what you will read will give you an unforgettable insight into our place in the universe.
Measure your coffee cup, your TV, your wife (but be careful what you say when you do it).
A few months back, I stepped on a nail and became concerned the next day and went to a doctor. He looked at my foot said it looked OK to him, then I pulled out the IR-thermometer and showed him the temperature of each foot, showing him that there was a 10 degree difference. "Wow, where did you get that", he said as he jumped up to write me a prescription for some robust anti-biotics.
There are more accurate IR-Thermometers, and ones that are very useful for finding specific leaks and cold spots, but there's nothing else as cheap and small and likely to be carried around and used casually and often in your daily life.
It's another set of eyes.
-AC