Between 3 and 7 (level dependent) are given when a total of 700 caps (or 350 with the Master Traderperk) are invested in Crazy Wolfgang's caravan at Canterbury Commons. You must speak to Crazy Wolfgang to receive the Stealth Boys.
In the Hubris comics utility tunnel, located on the floor by the northern wall of the northern room, along with the body of its previous user. At the four-way intersection, turn north, then east to reach the room.
Found in the offices and cafeteria. 1 on a desk in an office cubicle in the room at the back where the D.C. Journal of Internal Medicine is, 1 in the mainframe room, 1 on a bookshelf in the room where Nikola Tesla and You is found, 1 found in a cubicle left of the entrance in the northwestern most room of the Factory Floor.
The clear, see-through texture produced by stealth armor is slightly different than that of a Stealth Boy, and can be compared by hot-keying a Stealth Boy, and activating it while sneaking.
The effect lasts for one in-game hour, or 2 real-time minutes. If using an additional Stealth Boy when a previous one is still active, the duration of the stealth effect does not replenish - it "stacks", so the effect will last two in-game hours.
Before patch 1.5, it was possible to use the "set timescale to [multiplier]" console command on the PC to extend the Stealth Boy's duration to the desired time. Afterwards, it lasts 2 real-time minutes regardless of the timescale.
The use of the Stealth Boy while in combat with non-hostile non-player characters and then crouching can stop combat. The non-player characters usually revert to being friendly.
pc There is a glitch wherein activating a Stealth Boy causes the hair mesh of a character not wearing any headgear to appear on the Pip-Boy, or in random other locations near the character, while in 3rd-person view. This does not affect whether enemies will detect you. [verified]
xbox360 There is a glitch where activating a Stealth Boy and then traveling to D.C. ruins on the Duchess Gambit, the effect will still be active as long as 1 in game hour. [verified]
ps3 Occasionally, if you use a Stealth Boy and then open a save previous to using it and put it in any container (even owned ones), then walk out of the building, it disappears. [verified]