Do I need an Apple Watch?

No. Everything runs on the phone. The watch is recommended, since mirroring, haptics, and wrist logging are a big part of the experience, but it is never required. On a paired FTMS machine you get live speed, distance, and grip heart rate with no watch at all.

If you wear a Garmin or another non-Apple watch, the whole phone app works, and what you do on that watch still reaches Parameter. Those apps write your completed activities into Apple Health, and Parameter offers to import them into your history, so your AI reads what you actually did rather than only what it planned.

What you do not get is live heart rate straight from the watch. Those apps hand their data to Apple Health after a session rather than streaming it, and Parameter does not currently pair a Bluetooth heart-rate strap directly.

On a machine there is a way round it. Most Garmin watches can broadcast heart rate over Bluetooth exactly the way a chest strap does. Pair the watch to the machine’s console, and Parameter reads whatever heart rate that machine reports, which is what feeds the heart-rate chip, the zone gauge, and the drift alerts. Whether a console passes a paired strap’s reading through varies by machine, so it is worth trying rather than guaranteed. If you go this route, leave Parameter’s own heart-rate broadcast off, since it would have nothing of its own to send and most consoles pair only one strap at a time.