The Size Beam generators appear exclusively in Metallic Madness. They are usually fitted in corridors to shoot lasers down towards the ground. If the playable characters are caught in the beam, it will alter their size. The red lasers cause the playable character to become ⅔ of his original size. This will allow the playable character to run through corridors otherwise too narrow to pass though. The white lasers will cause the playable character to return to their default size.
In other media
Sonic the Comic
In Sonic the Comic #27, a midget version of Sonic from the near future encouraged Sonic into a Size Beam to make him small as well. This was done so that Sonic would be able to infiltrate a machine in the Miracle Planet's past to disable it and prevent it from turning the planet into a mechanical wasteland.