Diablo III- Skills Article LII: The Demon Hunter, Device Skills- Sentry

Sentry (10 Discipline): Create a crossbow turret that lasts for 30 seconds and attacks at your firing rate for 20% of your weapon damage.  You may only have one turret at a time.

The Device skill with perhaps the most iconic look, the Sentry is a useful little thing.  In short fights it’s unlikely to be terribly handy, since the damage is very low- but if you’re fighting a large number of mobs, or a protracted fight against a miniboss, rare, group of champions, or boss, it becomes quite worthwhile.  The duration is impressive and lets you pretty much just drop the thing and then forget it- as the turret’s not destructible.  Since you only get one at a time, it’s a lot harder to use the duration and indestructibility to your advantage when you’re having to move from fight to fight.

Spitfire Turret (10 Discipline): Create a crossbow turret that lasts for 30 seconds and attacks at your firing rate for 20% of your weapon damage.  It will also launch homing missiles at nearby targets at the same rate for 8% weapon damage as Fire damage  You may only have one turret at a time.

This is a pretty basic improvement over the Sentry.  While it has a few nice advantages- being able to target multiple enemies at once, some of the damage doesn’t get wasted if the target dies before the projectile arrives, things of that nature- it’s really not as great as it could be.  The extra damage is Fire, which is amply resisted, and it’s pretty small as well.  Still, if you specialize in critical hits, it’s that many more shots taken, and if you focus on rockets, this certainly puts out rockets.

Vigilant Watcher (10 Discipline): Create a crossbow turret that lasts for 40 seconds and attacks at your firing rate for 20% of your weapon damage.  You may only have one turret at a time.

Slightly more useful than the Spitfire Turret for protracted battles or boss fights, the Vigilant Watcher option mostly just means replacing the turret less often.  This can cripple your use of it if you happen to use this skill during regular fights, since it takes longer to get the option of placing a new turret.  Consider it based on when you’re using the Sentry skill.

Chain of Torment (10 Discipline): Create a crossbow turret that lasts for 30 seconds and attacks at your firing rate for 20% of your weapon damage.  You are attached to the turret by a tether which, rather than restricting you, deals 40% weapon damage every second to each enemy it touches.  You may only have one turret at a time.

This is probably the most useful form of Sentry for handling large numbers of mobs.  The tether damage is almost certain to be of more use than the attack damage of the turret, which is fine- sweeping slowly through groups of enemies and carving them to bits just by being opposite your plantable crossbow is a huge advantage, particularly with your ability to reduce enemy mobility and enhance your own.  Very much worth considering, even against bosses, as it’s just that much more damage.

Aid Station (10 Discipline): Create a crossbow turret that lasts for 30 seconds and attacks at your firing rate for 20% of your weapon damage and heals nearby allies for 1% of their maximum Life per second.  You may only have one turret at a time.

If you travel with a melee combatant, even a Templar follower, this becomes a very useful rune to tack onto your Sentry.  High-Life Barbarians will especially appreciate it, but nobody’s going to be at all dismayed about you picking this while you’re in their party.  This only gets stronger the more allies you have- but be aware that its range is limited, so in fights where everyone has to run around a lot (particularly Azmodan), it won’t be as useful.  Still, a nice side benefit.

Guardian Turret (10 Discipline): Create a crossbow turret that lasts for 30 seconds and attacks at your firing rate for 20% of your weapon damage and reduces the damage taken by nearby allies by 15%.  You may only have one turret at a time.

This one is virtually always superior to Aid Station, and is a huge boon to keeping your party intact.  If you work with any melee tanks at all this is going to be your favorite rune for this skill, and even if not, it could easily turn out to be superior to all the other runes.  Even if you don’t think you want it, give it a try- you could be very pleasantly surprised.