Broadcasting packets to a phone without a connection

Question

This is sort of an odd question, but I know it is possible.

I am trying to broadcast packets over a specific frequency and I want a phone running an application to pick up on these packets. The phone will not need a connection to any network to do this, but simply have it's wifi turned on. The broadcasting device does not need to get any information back from the phone and delivery of every packet to the phone does not need to be guaranteed, much like UDP.

Where do I start? Is this possible for phones without rooting them. Is there some kind of FCC regulation against doing this (over the standard wifi spectrum).

I know this is possible because it's exactly how routers tell a phone they are available to connect. Thanks in advance for any input.

Answer 1

I'm not familiar with iOS development although similar techniques may exist.

Without root

^{But requires coarse- and/or fine-grained location permission on Android}

You can use WifiManager.getScanResults() to scan for wireless router broadcasts.

The network "name" (SSID) and router MAC address (BSSID) are included in the results. You could broadcast these packets and encode data into these fields.

That said, I hope your messages are short as you'll be getting 38 bytes per packet (32 SSID bytes + 6 MAC address bytes).

^{Yes, some MAC addresses are special or invalid, but if you're just broadcasting and not actually using them, they can still transmit the data.}

With root

Depending on the wireless chipset and driver support, you may be able to put the device into "monitor mode" which gives you access to the raw packet data.

The main drawback is that there is no official support for it.

You might find some hacky ways to do this from a Google search but I wasn't able to find any universal solution that works on all (or even most) devices.