While making a Battle Smith Rock Gnome, I came to a similar question to this one about the Steel Defender, but saw it in another light; Though it is a construct, there is nothing in the stat block or artificer entry that states it does not require rest. While this is also true in the Monodrone entry, I do know that the warforged entry does specifically state that they have an ability called Sentry's Rest requiring them to effectively "sleep" for 6 hours.
As such, I was wondering if such constructs as Steel Defenders would require rest, or if one could combine the following two features to make an effective night watchman?
Vigilant. The defender can't be surprised.
Steel Defender (Artificer entry) […] If you are incapacitated, the defender can take any action of its choice, not just Dodge.
Best Answer
The Steel Defender need not sleep
It is immune to exhaustion, it can stay up all night and party like a steel rock star.
Not only that, it should make a reasonably good night sentry, since it has darkvision to 60 ft and gets your proficiency bonus x 2 to Perception and Passive Perception checks.
The Steel Defender is immune to exhaustion, as noted in its stat block.
Xanathar's provides some rules for going without a long rest:
Since the Steel Defender is immune to exhaustion, it can just choose not to sleep.
Of course, if the Steel Defender doesn't sleep, it doesn't get a long rest, and while it doesn't suffer exhaustion, it doesn't gain any of the benefits of a long rest, such as regaining hit points or spent Hit Dice. However, you can repair it yourself, if necessary, or just make a new one.