The paper presents a study of the noise level of accelerometer data from a mobile phone compared to three commercially available IMU-based devices (AX3, Equivital, and Movesense) and a marker-based infrared motion capture system (Qualisys). The sensors are compared in static positions and for measuring human micromotion, with larger motion sequences as reference. The measurements show that all but one of the IMU-based devices capture motion with an accuracy and precision that is far below human micromotion. However, their data and representations differ, so care should be taken when comparing data between devices.