Can they be made to announce their presence somehow using layer 2 frames without them be connected to any network or access point?
Can their MAC address be found?
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You may be interested in this question, the answers, and comments. Otherwise, end-devices and consumer-grade devices are off-topic here.– Ron Maupin ♦Commented Mar 16, 2016 at 14:51
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This really isn't a question about any particular device, it is more of a question regarding how 802.11 operates.– YLearnCommented Mar 16, 2016 at 18:40
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2 Answers
Do wireless devices such as smartphones transmit beacon equivalent frames such as APs do?
A wireless client does not transmit beacon frames. However if a device is configured to provide service (i.e. tethering, etc), then it is acting as an access point and would transmit beacons.
Can they be made to announce their presence somehow using layer 2 frames without them be connected to any network or access point?
Not only can they, they do so on a regular basis. Client devices use "probe requests" to aid in discovery of nearby networks. This would be somewhat similar to the device shouting out "Are there any networks nearby?" For more details, feel free to reference this other question about How do wifi clients detect SSIDs from APs?
Can their MAC address be found?
If they use their real MAC address, then yes. Some devices have started using fake MAC addresses when probing networks, however this can cause a number of problems in certain wireless environments.
802.11 specifies clients listen for AP beacons. They don't broadcast anything.
However, real world implementations (Windows, iOS, etc.) actively hunt for known SSIDs when they aren't associated. These probes will broadcast a MAC, but in the case of recent-ish iOS, Apple randomizes the MAC for these probes. (to thwart attempts at passive tracking)
