Location-based services have become popular as smartphones are able to listen to the faint GPS (or GLONASS) signals and figure out where you are in relation to other things. But roofs and walls can block out those satellite signals, leaving you on your own once you enter a building.

Now, many mapping applications are intended to get you to a building, so, once you’re there, well, you’re there – mission accomplished. But, as any of you that go to conventions will know, even within the building, it can still take a map to navigate the exhibition floor.

Rohm, in cooperation with iSiD, has announced the Guidepost Cell to address such indoor navigation challenges. The cells make up the nodes of a network that can detect the presence of a smartphone with WiFi turned on and then figure out which is the closest cell. Because it passively looks for telltale WiFi signals, it doesn’t have to emit a constant beacon, reducing power consumption considerably.

Because of this miserly behavior, they can operate without external power – by harvesting the indoor light. They do this using dye-sensitized cells, something we’ll cover in more detail in the future. They’re essentially “indoor” solar cells.

This means that a network can be established more or less by distributing these Guidepost Cells and turning them on. An application on the phone can then detect the network and, coupled with an indoor map, show you where you are or where you want to go or send you a message.

You can find more detail in their release.