Placing a linked portal underneath a camera will cause it to be detached, followed by a warning (only in Portal) from GLaDOS, in which she refers to the camera as "testing apparatus."
The cameras can rotate 360 degrees, and they follow the players' movements within Test Chambers.
As well as its main video camera, the security camera appears to have a small device attached on the side, which possibly monitors infrared radiation from the body heat of living creatures.
Not a single security camera is featured in any of the maintenance areas or observation rooms of Aperture Laboratories, and it is therefore unknown how, or even whether, GLaDOS can monitor Chell's movements during her escape in Portal. Her calls through the Speaker System do not strongly connote that she is able to monitor the escapee. It is possible, however, the speakers also have microphones, so she can hear footsteps and use information of the microphone's location and loudness of the footsteps to determine where Chell is.
As seen on ApertureScience.com, the image of the security camera feed is green, despite its lens being red.
One of the unknown Aperture Science employees in Portal 2: Lab Rat states that the cameras, in fact, contain cameras inside them (although this statement may have been a paranoid delusion of Doug).
GLaDOS states during the Cooperative Campaign "Did you know we originally used these cameras to capture moments of intense pain and agony in test subjects? If the subject survived the test, we let them purchase the pictures for $5. If the subject died, we gave the photo to their next of kin free of charge. The photos weren't as popular as we had hoped, so we repurposed the cameras." Whether this is truthful or meant to initiate an emotion of fear in the player is unknown.
Several detached security cameras can be found in Rattmann Dens, along with the message "She's watching you."
An Orange Box Achievement, "Camera Shy," requires the player to detach all security cameras from the walls. This is only possible with security cameras attached on concrete walls (thus disregarding those fixed into metal) and not before the ASHPD has been acquired. There are 33 total.