Portal ARG

The Portal ARG, or , was introduced as an easter egg in the March 1 Patch. The notes released along with the patch read "Changed radio transmission frequency to comply with federal and state spectrum management regulations", and accompanying this was a new achievement, "Transmission Received".

In order to acquire the achievement, players were required to collect a Radio in each test chamber, and carry it to a specific location. The red light on the radio would change to green when the correct location was reached, after which the default music would change to a series of beeps, similar to. If a player carried the radio carried through a Material Emancipation Grill, a different sound would play. It was later discovered these sounds, stored in 26 separate WAV files, contained hidden images that could only be accessed by using software.

In addition to images, the WAV files also contained brief messages in Morse Code, as well as a phone number and a username/password combination. It was eventually discovered that dialling the number using an analogue modem lead to a GLaDOS-themed which, when accessed using the aforementioned username and password, revealed more images and other data that hinted that Portal 2 was forthcoming.

On March 3, another patch was released that changed the ending of Portal, and this was considered confirmation that Portal 2 would soon be released. On March 5, three days after the commencement of the ARG, the sequel was officially announced.