A bot would send a packet; the packet is one smell molecule of information containing anything you want to know about a bot except DNA things. The packet requires a) nothing or small amount of energy or maybe just as a waste product. The packets would merely change ref info (including the eye returns, meaning a bot could see the smell, or at least sense it/ it may be best to actually use a nose to sniff for these packets). A bot could attempt to decifer the packets for information to determine the next action, but the chances of failure are determined by the rate the packets decday, and the mutations that occur as they decay. The production of the packets would essentially be involuntary, as smell happens from waste and everything, and nothing in the environment should be able to create these packets, unless we want to add smell to everything.