Originally Posted By: hikermor
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Signal mirrors don't work too well when one is deep in a gully,but PLBs do (note to self - perhaps consider acquiring a PLB next time when walking in a gulch).

Per this 2008 ACR ResQfix 406 MHz PLB test in eight Zion slot canyons, PLBs can work in slot canyons, but nowhere near as well as in open ground - the location accuracy was far poorer, and in one of the eight canyons, the PLB was not detected during the test (which seems likely to have been 2 hours, but not explict.) In one of the 7 successful cases, the location accuracy was 10 miles in 9 minutes, 3 miles after 9 hours, and 2 miles after 17 hours.

For those wanting meatier details than the summary article linked above, here is the download link to the 16 pg test report by Kevin Killian
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A signal mirror should backup a radio distress signal, like a 406 MHz PLB (ACR PLB) (Ocean Signal PLB)