Tech proximity mine

Tech proximity mines are, as the name implies, mines placed as a 'side effect' of using tech talents like Sabotage, Overload, or Damping. They are the closest your squadmates get to being able to use grenades, but while proximity mines are not as effective, there is an unlimited supply once a tech talent has recharged.

Proximity mines will usually explode instantly if you are using tech talents specifically on an enemy. When enemies are approaching or about to appear, using one of these talents (say on a wall or nearby obstacle) allows you to effectively put a minefield in their path which will detonate once they get close enough. Proximity mines, unlike grenades, do not have a timed fuse, but they usually vanish once the combat session is over or if no enemies appear for an extended period.

Tali appears to use a tech proximity mine during the ambush in the alley.