An IMU bundles an accelerometer, with a gyroscope, which senses rotation rate, on one MEMS chip; nine-axis parts add a magnetometer for heading. The raw outputs are reported over I2C or SPI, and on-chip logic can detect taps, steps, free fall or simply whether the device has moved at all, raising an interrupt so the main processor can stay asleep.
In IoT the IMU is the sensor behind wearables, asset tracking tags that only report when a shipment moves, vibration monitoring on machines, and tilt or tamper detection on fixed equipment. Turning the raw streams into a stable orientation requires sensor fusion, because accelerometers are noisy under motion and gyroscopes drift over time. The main trade-offs when choosing a part are noise, sampling rate and current consumption in its always-on detection modes.
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