The tracking bracelt is a not needed as Google download a Covid-19 tracker on everyones phones months ago, just needs to be turned on(or off if you don't know its on already) don't know about iPhones.
The problem with the phone trackers is many guests don't carry their phones around because they don't have roaming turned on so they are useless to the guest. No way to enforce someone carrying their phone 100% of the time but a bracelet that can't be removed is more foolproof.
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