Nobody wears ankle bracelets to warn kangaroos or anything or anyone else that they are near.
Some criminals on parole or on bail have to wear ankle bracelets that can be tracked to prove they have remained at home, as decreed by their bail conditions or, if on parole, that they have only been to places they are allowed to go.
I assume Glitterbag imagined kangaroos in her insult because Builder is Australian, or she thinks he is, and kangaroos are emblematic Australian fauna.
She’s just slurring Builder by saying he’s dangerous enough to require that there be warning broadcast so living beings can get away and avoid him.
It’s a stupid pretty much meaningless insult. You’re overthinking it