"Electromagnetic pulse grenades damaging to electronic equipment."
Each blast deals 50 EMP damage, stunning for 25 seconds.
After being stunned, mechanoids become 'Adapted' and gain immunity against further stuns for 2,200(36.67 secs). Immunity is applied on stun, and will not be extended by stunning an adapted or already stunned mechanoid.
They can be crafted, purchased or looted from dead raiders.
Using EMP grenades against friendlies counts as an attack even if they aren't hurt.
EMP grenades are very effective against centipedes. Their slow move speed and large size make them easy targets. They have a very high damage potential, so even temporarily shutting them down will give your colonists an advantage in a battle.
It is a good idea to manually aim EMP grenades instead of letting your colonists do that. They will not lead the targets and will not attack targets which can only be hit by area of effect. Repeated applications while the target is already stunned will cause stun adaptation to happen earlier, while not affecting stun time significantly.