A neo-pixel ring. Start with an ATtiny45 (in the smallest packaging), batteries to get to about 5 volts, 1-5 of the adafruit neopixels, and add a sensor like accelerometer, gyro, barometer/temp and maybe a switch if the sensor can’t be used for a wakeup. You can use RETMA colors or just have it work like a compass.
There is an ATtinyX5 neopixel library, and I’ve done a bitbang I2C library.
If preferable, a bracelet or thin band. Or even inside a straw something like a magic wand.