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The pictures of flight data recorders show that the location beacon (pinger) is outside the main protection encasement:

enter image description here

Is it really a good idea to keep such a vital instrument unprotected? Or is that round metallic thing strong enough to resist impact and fire?

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    $\begingroup$ it doesn't need to survive a fire (it'll sink) only impact with water $\endgroup$
    – ratchet freak
    Commented Apr 7, 2014 at 10:41
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    $\begingroup$ Also, the more stuff you cover it with, the harder it may be for the "ping" to get out. $\endgroup$
    – fooot
    Commented Apr 7, 2014 at 15:17

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Is it really a good idea to keep such a vital instrument unprotected? Or is that round metallic thing strong enough to resist impact and fire?

The casing of the ULB is itself designed to be strong enough to withstand the forces expected when an airliner crashes into an ocean, lake or large river (which are the only circumstances where a ULB is useful).

See teardown video starting at around 4:45

Copies of the relevant standards cost $70 each. However, a 1968 report from the early days of ULB development says

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As voretaq7 notes in a comment: ULBs need to be external to the FDR/CVR canister because they need to have batteries changed regularly without affecting the integrity of the data recorder canister.

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    $\begingroup$ The "pinger" also needs to be replaceable/serviceable - they have a battery with a limited shelf life which is much shorter than the service life of the recorder. Were the ULB located inside the main body of the recorder the entire assembly would need to be returned to the manufacturer to be opened and services - this design allows airline maintenance to replace the ULB without compromising the seal on the data portion of the FDR. $\endgroup$
    – voretaq7
    Commented Apr 7, 2014 at 15:51

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