Tonic Clonic Seizure Detected

Benjamin had a tonic-clonic seizure this morning, so I thought it would be useful to describe how OpenSeizureDetector performed in detecting it.

What Happened

  • Benjamin sat up and contorted in an unusual way – head looking up and to the left.
  • Sandie saw this on his video monitor and recognised it as a fit and set off up the stairs to check him.
  • When she found him, Benjamin was lying on his back with arms shaking, but not out stiff (his elbows were bent).
  • It was not one of his worst tonic-clonic seizures – he was not paralysed after it, just needed to sleep it off for a few hours.
  • OpenSeizureDetector alarmed as expected.

OpenSeizureDetector Performance

    • Sandie spotted the seizure using the video monitor from Benjamin’s odd behaviour before OpenSeizureDetector did – this is because OpenSeizureDetector needs the shaking associated with a seizure to detect it, but Sandie spotted the odd movement before the shaking started.
    • The first OpenSeizureDetector warning sounded about the time Sandie reached his bedroom.
    • The warning re-set unepectedly.  I think this was Benjamin falling bakwards, resulting in  a lot of low frequency movement, which the detection algorithm assumes is not seizure-like movement..
    • About 30 seconds later the warning re-initiated followed by full alarm.
    • When the full alarm sounded, Benjamin was lying on his back with arms shaking, but not out stiff (elbows bent).
    • Two full alarm initiations occurred before the seizure detector re-set as the movement subsided.
  • The spectra of the alarm and warning conditions are shown below.
  • The initial warning occurred at a peak frequency of 7 Hz. The full alarm occurred with peak movement at around 4-6 Hz.
  • These spectra are consistent with the type of movement OpenSeizureDetector is set up to detect – an excess of movement in the 3 to 8 Hz range compared to the rest of the spectrum.


  • It is encouraging that OpenSeizureDetector detected a tonic-clonic seizure as expected – the spectrum is consistent with the movement the system is designed to detect.
  • The re-set when Benjamin fell backwards is not what I had expected to happen.   I think we need to add some hysteresis so we have to see a reset condition for a few analysis periods before resetting the alarm.   This will increase the false alarm rate though…..

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