Wearables are devices worn on the body: watches, fitness bands, VR headsets and AR glasses. What they share is proximity: a screen or sensor closer to the person, and therefore closer to their attention, than a phone in a pocket.
The case with an established track record is the smartwatch notification, mostly because it rides on infrastructure the customer already owns and has already opted into. A boarding pass or a queue call on the wrist is genuinely better than the same thing in an app.
The caveat is that every other wearable case in retail depends on penetration that does not exist. Designing an experience around AR glasses means designing for a fraction of a percent of visitors, and a venue-supplied headset means distributing, cleaning and collecting hardware, which caps throughput at a handful of people an hour.
The reliable rule for now: build for the device the visitor already carries and treat wearables as a delivery surface for something small and timely. Anything requiring the venue to hand over hardware is an event activation, budgeted per visitor, not a channel.