Bumping/file sharing technology

Guys,

There are a number of applications on the market that allow Android phones to exchange files or some other information. Those applications usually rely on two Android devices being in close proximity and detecting each other's presence. I do not think that they use bluetooth communication to send signal to each other since bluetooth can be off and it would take some time to activate it so bumping would take longer than it does in those applications. Thus those apps have to use some other sensors that most of android phones are equipped with.

Do you have any idea of what those sensors are and how the phones become aware of each other's presence?

Thank you in advance

http://bu.mp/faq

E-Oreo,
thank you for the quick reply. The theory behind how this works with the backend servers and stuff seems to be clear, what is not obvious is how exactly the phones detect each other, that is through which sensors. The most obvious candidate would be bluetooth, but it is not since it is not needed to be enabled for the bumping to work.

Thanks again,
cromartie

They don't actually detect each other. The accelerometer in them detects the motion of a "bump". When it detects a bump it sends a message to the central server. If the central server receives two messages from the same location, it assumes the phones were bumped together and sends both of the phones a message telling them that.

Thanks you for clarification - this actually makes sence now. But does it mean that the GPS has to be switched on for this to work? Because if it is not on on either of the phones then the apps would have to pop a message that it needs to be switched on for it to work thus making the bumping action more clumsy.

There are three ways a cell phone can figure out where it's at; one is using GPS, which is by far the most accurate, but requires GPS to be turned on and a clear line of site to the sky; a second is triangulating its position using nearby cell towers, which is less accurate by virtually always enabled and doesn't need line of site to the sky; and a third is using nearby WiFi networks, which can give a general location if you actually connect to them and a relative location if you don't.

Thanks a lot for the information - good to know there are several options