Molecular communications systems use the presence or absence of a selected type of molecule to digitally encode messages. The molecules are delivered into communications media such as air and water for transmission. The technique also is not subject to the requirement of using antennas that are sized to a specific ratio of the wavelength of the signal. Molecular communication signals can be made biocompatible and require very little energy.
The technique has potential applications in environments where electromagnetic waves cannot be used, for example in underground structures such as tunnels, pipelines or in underwater environments. 
Researchers demonstrated the use of evaporated alcohol molecules to carry messages across several metres across open space and successfully decoded the message on the other side. The presence of molecules encoded to digital 1 and their absence encoded to 0. The hardware cost around $100.