Arduinos wirelessly aware of one another's presence?

Hi,

I need to have two very small arduinos to be wirelessly aware of the presence of one another.

All I really need them to know is the “ID” of each other… so simply transmitting an ID number at periodic intervals (like every 30 seconds) should be sufficient. It would be a cool nice-to-have to have them know roughly how many meters away the other is, but this isn’t a requirement.

What I’m looking for is a low-cost, simple module (ie chip) that enables this type of super basic communication. Simply broadcasting an ID and listening for the IDs of others is what I’m after. Being aware of one another in the range of up to 20-50 meters would be sufficient (we’re not talking kilometers here).

I’m working on an arduino prototype but would eventually build my own PCB with this feature onboard. It’s also really important the solution be really small. We’re talking wearable devices here.

What is the right solution? An RF transceiver? A wifi beacon that simply pushes out the name of a wifi network? Can you link to any existing modules or chips I can get started with to prototype this? An XBee seems too expensive and large…I’m looking for a solution that can work for commercial production. Is BLE the solution? It seems BLE is specifically device → phone communication, not device <-> device.

Thanks a bunch!

Define low-cost!

If this has to be a wearable device, power consumption is probably more important than size. BTLE may be a bit more expensive in the Arduino world but it's very low power and already includes the identification of available devices. And a phone is also a "device" :). You just have to ensure that your BTLE module is able to be master and slave. So it may scan for devices within reach and send it's own identification.

The nRF24L01+ modules have an antenna on the pcb.

The receiver must be on all the time, some receivers need 10mA. Is that too much ?

nrf24l01+ modules are small too. http://yourduino.com/sunshop2/index.php?l=product_list&c=12

If they only need to be aware of each other and not exchange data then you could maybe us bluetooth modules and let them scan for (but not connect) other BT modules within range?