How do you know when you need a break?

One highly consistent signal is the growing feeling of "I absolutely cannot take a break right now", entering the burnout phase when I start feeling frustrated or angry when someone else suggests I need to take a break. I suspect this signal is reliable because it correlates with how much I'm over-indexing on the Current Critical Thing, leading to reactive & pigheaded actions and the loss of broader perspectives.

I bought a Garmin watch for the body battery feature. I track my usual body battery throughout the day. If it's low, then I could use a break.

At 3 PM, it's normally 50. If it's 60, I push myself. At 30, I take a nap.

Naps are good way to reenergize and they keep you from dumping more energy on other stuff (e.g. HN, Facebook). Otherwise, I like just watching music videos. Some would say meditation, but paying attention to music is a form of meditation for me.