The personal Phaser is the smallest of the standard issue weapons used by most Starfleet personnel. It has a variety of power settings and frequently proves invaluable for personal defense in hostile situations, as well as for several other uses.

The actual term, phaser, is an acronym for PHASed Energy Rectification. Personal phasers were first developed by Starfleet in the 23rd century as a defensive beam weapon for use by personnel heading into uncertain situations on alien worlds.
There are actually three classes of personal phaser. The Type-1 phaser is a hand-sized unit, easily concealed, and hence ideal for use on diplomatic or similarly sensitive missions, where it would be unwise to appear heavily armed. Type-2 phasers are larger, more powerful weapons issued to personnel heading into known hostile environments. The Type-3 phaser rifle is only issued in special situations.
All phasers are capable of firing beams of varying power. The settings include 'stun', to render an organic target unconscious; 'heat', for warming objects such as rocks for use as heat or light sources; and 'disruption', which destroys objects and almost any known life form.

Although the Federation is a peaceful organization, personnel carry weapons in order to defend themselves from the numerous hostile life forms they are likely to encounter. The versatile phaser type -2 can be used to lightly stun a human or to blast through rock.

The phaser type-2 is an intermediate size hand-held weapon, it lies between the smaller hand phaser, or phaser type-1, and the much larger phaser rifle, or phaser type-3.
The phaser type-2 has a significantly increased power and range in comparison to the phaser type-1, with 16 settings available - twice as many options as are available with the type-1.
By 2366, pistol phasers are a single unit almost like a 20th century flashlight. The firing button is on the top and is operated by the thumb rather than at front of the pistol grip and operated by the forefinger, as was the case with earlier models. Close to the trigger are controls which can be used to vary beam width and intensity.
The model of phaser type-2 in use by 2366 has 16 settings, ranging from light stun to disintegrate. The lowest, or stun setting, is designed to cause temporary unconsciousness in humans for up to five (5) minutes, while setting 16 causes major geological displacement and can even damage objects within shields. Intermediate settings can be used to drill holes, cut an object into pieces, or merely heat an object such as a rock to provide warmth.

Charging the phaser
As with the phaser type-1, energy is stored within a sarium krellide power cell which can be replenished when empty (Read Nickel Cadmium). Personnel on board starships can charge their phasers through the standard power taps of the electro-plasma system. Away from the ship, portable bulk sarium krellide units are used. The power cell of the phaser type-2 measures just 10.2 x 3.0 cm and holds 4.5 x 10⁷ MJ of energy.

Explosive energy
Due to the potentially dangerous nature of the phasers, there are a number of safety interlocks built into the system. On board ship, a subspace transceiver array built into the phaser maintains contact with the ship's computers to restrain power levels to below those which would damage the ship - generally limiting them to heavy stun. In addition, the phaser also contains safety interlock, a code processor which, amongst other functions, can personalize phasers for use by certain personnel only. Key-press combinations of beam width and intensity controls are used to configure the phaser's safety condition. Even when not in use, a phaser constantly trickles energy. Normally, the weapon is prevented from overloading by the safety interlocks, but this makes it possible, in extreme situations, to set a phaser on overload, turning it into a makeshift bomb. If the phaser is not allowed to give off energy at a defined rate, it will sound a warming noise for a few seconds, and then explode, causing the death and destruction of everything within a radius of several meters.
This particular model is used until 2365, after which a slimmer, sleeker version comes into general use.