Oneiros is a miniaturized device capable of recording multiple biological parameters in laboratory and field conditions for unprecedented periods of time. This new electrophysical measurement system designed for conducting research on freely moving small animals is capable of recording several days up to 26 electrophysical signals (EEG, EMG, ECG, EOG or LFP), metabolic (3 temperature channels such as brain, body, and ambient) and behavior via tri-axial accelerometer.