Can we use tools to measure our energy level fluctuations?

Currently there exist biometric sensors that can measure things like (i) our heart rate, (ii) how many steps we’ve taken during the day, and so forth.

Question: Do there exist biometric sensors that can measure fluctuations in our energy levels?

Note that when I speak of “energy levels,” I’m not referring to anything spiritual. Instead – the way I’m using the phrase – if someone is feeling a high “energy level,” he will feel that he has a relatively high capacity to perform physical work, socialize with people, and so forth. On the other hand, if a person is feeling a lower “energy level” (in the way that I’m using the phrase), he might just want to chill out by himself or go to a sleep. :slight_smile: