SeizeIT2 is a multicentre (5 European EMUs) validation study of the Byteflies Sensor Dot: behind-the-ear EEG, single-lead chest ECG and module accel/gyro (plus a deltoid EMG channel, out of scope) recorded alongside clinical video-EEG in 125 refractory focal-epilepsy patients (adult + paediatric), ~11,640 h with 886 annotated focal seizures. BIDS on OpenNeuro (ds005873 v1.1.0), CC0.