[themoonisachees]

A modern smartphone, no, not currently. Feature phones maybe, if made specifically with low-power parts.

Personally I'm interested in putting this in a watchy [0], that can get around on tens of microwatts average consumption because of deep sleep states and an e-paper screen.

[0] https://watchy.sqfmi.com

[rsaxvc]

That's more the scale I was thinking .You'd still need a rechargeable battery or large cap to run the ESP32 in any useful mode.