In Deus Ex: Human Revolution for the PC, PS3, and Xbox 360, there are seven hidden Praxis Kits you can find throughout the game that will give you free upgrades to your augmentations.
Search the following locations to find the hidden Praxis Kits.
Sarif Manufacturing Lab – After the Assembly Line, use the elevator near the Factoring Labs. After exiting the elevator, you will find the first Praxis Kit in the hallway.
Detroit City Sewers – In the northern sections of the Detroit Hub, go down into the sewers and look at the map. Look in the eastern corner for a dead-end slightly south of a sewer entrance. Go there, and you will find a light wall. Upgrade your augmented strength in order to break through the light wall and find the Praxis Kit.
Hengsha Sewers – On your map, look for a U shaped section of sewers below the Huang Hua Hotel. There is a light wall in this section that you can break through using the upgraded strength augmentation to find the Praxit Kit, next to some pain killers.
Hengsha Court Gardens – In the elevator shaft, climb down to the bottom and look underneath the elevator to find the Praxis Kit on the floor.
Tai Yong Medical – On the second floor of the Tai Yong building, look for a hallway on your left, and look for  a door that leads to another corridor with two offices. The Praxis Kit is in the first office in the corner.
Picus – Inside of the news building on the main office floor, you’ll see an empty area with a lot of cubicles. Go to the middle row of cubicles, and look near the center desks to find a Praxis Kit.
Derelict Row Apartments – Go into the apartment building in Derelict Row and go up to the third floor. You’ll see the Praxis Kit near a dead body.