The Mobile Emitters are a set of agents created by SnowFox for Creatures 3 and Docking Station. They were once available at Dragon Keep Creatures.
This is a set of 6 floating thingamabobs that emit various CA values. There's one for each creature home (Norn-light blue mist, Ettin-yellow mist, Grendel-dark green mist), one for heat (white), one for soil moisture (dark blue), and one for nutrients (light green). The latter two can be placed in "dead" metarooms and, provided the room type is soil, enables plants to grow there.
Essentially, they work like the smell emitter in C3, except they float, and don't make noise. These objects float wherever you put them, and constantly output CA. Creatures aren't allowed to touch them, so you don't have to worry about the Ettins running off with them ;)
Sprites built off of the DS camera units...Yes I know they suck, I couldn't get anything else to look any better ;P