Staser

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.

Usage
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. A posthumous effect could make unrecognisable the corpse. (TV: The Deadly Assassin)

It would seem a single staser shot could kill a Time Lord outright and ensure that regeneration could not take place.

Stasers were ineffective against Sontaran armour, (TV: The Invasion of Time) and against androids of Kraal manufacture. (AUDIO: The Oseidon Adventure)

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.

Before his death, Andred showed his wife Leela how to operate a staser. (AUDIO: Extermination)

Instances of use
A staser wielded by Commander Maxil was used to stun the Fifth Doctor. (TV: Arc of Infinity)

A Castellan 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. (TV: The Five Doctors)

A staser sniper rifle was used in the assassination of the Lord President by Goth. (TV: The Deadly Assassin)