Staser weapons were the standard armament of the Chancellory Guard on Gallifrey. The Guards were normally equipped with staser pistols, although staser rifles were also occasionally used.
Stasers had both lethal and non-lethal settings, and fired an unspecified type of directed energy. They were relatively harmless to inorganic matter but caused massive tissue disruption to living creatures. The corpse would be unrecognizable upon examination. (The Deadly Assassin)
According to one account, a staser was a type of regeneration inhibitor, with a single shot being able to kill a Time Lord outright and ensure that regeneration could not take place. (The Ancestor Cell) However, stasers could be modified to allow for regeneration, as the Eleven used to torture Volstrom by inducing multiple successive regenerations. (The Side of the Angels) Similarly, the sidearm of the President’s personal security did not have a stun setting though a Time Lord shot with it could regenerate. (Hell Bent)
Stasers were ineffective against Sontaran armour, (The Invasion of Time), androids of Kraal manufacture, (The Oseidon Adventure) and Daleks. (The Apocalypse Element)
Staser pistols apparently come in different versions. Those seen after the Sontaran invasion were significantly larger then those seen before.
The stasers issued to Chancellery Guards and to security personnel were coloured red, but Castellan Spandrell and Chancellor Goth both used black pistols. (The Deadly Assassin)
Before his death, Andred showed his wife Leela how to operate a staser. (Extermination)
Stasers were used during the Last Great Time War. Children in the First Segment of the War sorted out staser bolt chargers in munitions factories. (The Stranger) Stasers were devolved into machine pistols on the Neverwhen planet front as a result of time phasing. (The Neverwhen)
Instances of use
A staser wielded by Commander Maxil was used to stun the Fifth Doctor. (Arc of Infinity)
Jerricho supposedly kept a small staser hidden on his person and was shot dead by security personnel whilst using it to attempt an escape during Borusa’s Death Zone gambit. (The Five Doctors)
A staser sniper rifle was used in the assassination of the Lord President by Goth. (The Deadly Assassin)
Coordinator Narvin was given a staser for a mission in Earth’s past. President Romana forbid him from using it to stun or kill humans. He shot a wall to impress the local people and he promised to gift it to Sol in exchange for her help. (Intervention Earth)
Commander Roxita and his Capitol Guard used stasers in vain against the Vashta Nerada on Synthesis Station. Within the Doctor’s TARDIS, the Eighth Doctor found that Roxita’s staser had been infested by the Vashta Nerada. (Day of the Vashta Nerada)
During his invasion of Gallifrey following his banishment by the Doctor, Rassilon killed his successor as Lord President with a staser, reclaiming his gauntlet and the title of Lord President. (Supremacy of the Cybermen)