Water, wet skin and marginal reads

Detuning, not damage

An antenna is tuned to resonate at a specific frequency, and that tuning depends on what surrounds it. Water has a high dielectric constant, so a film of it on and around the coil shifts the resonant point away from where the reader is transmitting. Less energy couples across, and a transaction that previously completed with margin to spare now sits at the edge. Nothing is broken; dry the band and it behaves exactly as before.

Pressing harder makes it worse

The universal instinct when a band does not read is to press it flat against the reader. On a wet gate this is precisely wrong: it squeezes a continuous water film between band and reader and puts the wrist directly behind the antenna, adding both effects at once. Holding the band a centimetre clear reads more reliably. It is counter-intuitive, it works, and it is worth putting on the sign at any pool entrance.

Salt water is a stronger effect than fresh

Dissolved salt makes water considerably more conductive, which increases both the detuning and the absorption. Bands at a beach club therefore read marginally worse straight out of the sea than bands at a pool, and the difference is enough to matter on a reader that was commissioned dry indoors. Beach properties should be testing at the water's edge with a band that has actually been swum in.

Commission wet, once

The single most useful commissioning step in this category costs ten minutes: take a production band, soak it, put it on a wet wrist, and present it to every reader type on the property in the position guests will actually use. Any reader that is marginal under those conditions is a reader that will generate complaints in August. Adjusting it in April is a job; adjusting it in August is an incident.