The warning sent to Abdulkarim al-Ismail’s Facebook came just moments before the warplanes would fly overhead and drop their load. He knew he had eight minutes at most to move his wife and two children down the basement.

When the thud came, it was close, closer than he had calculated. The building rattled and the windows shattered.

His neighbour down the road had not seen the message - the crucial window between life and death - and was killed in the front room of his home.

Mr Ismail, a teacher in the city of Saraqeb in the northern Syrian province of Idlib - the last-remaining rebel-held territory in the country - has for years relied on the warning system to stay alive.

The technology, developed by the start-up Hala Systems, works by detecting aircraft using remote sensors on the ground in Idlib and machine-learning algorithms, which look at the speed of an aircraft and its usual flight pattern.