What's this?

Kids picked this up off the floor at Llandegla and handed it to me when we got home. It wasy "USB" on it, but I can't see that there's anything complex about it. Is it just a speed sensor magnet or similar? Hopefully not valuable, but once I know what it is I might post it to the Llandegla facebook page in case anyone is desparately wondering where it is!
[Edit - link to photos now removed as the issue is solved]
[Edit - link to photos now removed as the issue is solved]
2015 Canyon Nerve AL 6.0 (son #1's)
2011 Specialized Hardrock Sport Disc (son #4s)
2013 Decathlon Triban 3 (red) (mine)
2019 Hoy Bonaly 26" Disc (son #2s)
2018 Voodoo Bizango (mine)
2018 Voodoo Maji (wife's)
2011 Specialized Hardrock Sport Disc (son #4s)
2013 Decathlon Triban 3 (red) (mine)
2019 Hoy Bonaly 26" Disc (son #2s)
2018 Voodoo Bizango (mine)
2018 Voodoo Maji (wife's)
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Hard to see how big it is.
https://www.ebay.co.uk/itm/264415237032
I have the same lights and have lost the end cap on more than one occasion.
They cost about £3 to buy a replacement.
I'll consign it to the bin!
2011 Specialized Hardrock Sport Disc (son #4s)
2013 Decathlon Triban 3 (red) (mine)
2019 Hoy Bonaly 26" Disc (son #2s)
2018 Voodoo Bizango (mine)
2018 Voodoo Maji (wife's)