> It's a scummy practice, sure, but hiring two things as a package isn't illegal in itself.

I believe this would technically depend on whether one is employed or self-employed.

Only self-employed people are generally obligated to provide tools of their trade; whereas, personal tracking strongly implies employment. It shouldn't be both. (This all may depend on jurisdiction and specific circumstances, obviously)

Given that the article clearly says the person was employed before being required to download an app, this also feels like a breach of contract by the employer.

In your terms: They employed the worker, not the worker and their phone.