Messages are compressed and encoded as WiFi access point names (SSIDs). While this approach allows for very short messages only – so short, in fact, that it makes Tweets look verbose in comparison – it has a number of interesting properties:
• Communication is inherently local. This means that when you go somewhere, and there's a message in the air, it refers to where you currently are. Relevance is defined by where you are right now, not by who you're following on Twitter, which Facebook groups you're in, or who's in your Google+ Circles.
• Communication is anonymous.
• Messages do not travel accross the Internet, therefore:
• Messages can not be monitored from far away.
• Broadcasting messages is robust towards Internet outages. However, broadcasting can be inhibited locally using a WiFi jammer.
• Broadcasting messages is free.
• It even works without a SIM card.
• There are no accounts or personal information.
• Messages are volatile.
Although in practice, SSID may only contain a handful of ASCII characters, Ahoy can be used to send messages in any language, using any script defined by Unicode. However, message lengths vary depending on the language a message is written in. Specialized language packs which employ Huffman coding are used to maximize message lengths for most languages, resulting in message lengths of 45 to 55 characters on average. Ahoy chooses the most compact encoding automatically, falling back to UTF-8 or UTF-16 if no appropriate language pack is available.