Wearable devices

A shape held by pressure between two anatomical points works when those points sit where the designer assumed. Pelvic geometry varies enough that the same device stays put for one person and shifts constantly for another, and no amount of design solves it universally. This is the main reason reviews of these products disagree so sharply.

Remote operation is the usual reason for buying one, and it introduces its own considerations. A radio remote works over a few metres and needs no account. An application over the internet works at any distance and involves a service, an account and whatever data policy sits behind it. That is a privacy decision rather than a technical one, and it is worth making deliberately.

Runtime matters more here than in any other format, because the device is worn for long periods at low settings rather than used briefly at high ones. Noise also behaves differently: fabric muffles high frequencies well and low ones poorly, which the noise page explains.

• Whether the shape is held by the body or by a garment.
• Runtime at a middle setting, not at the lowest.
• Whether the control is on the device, a remote, or an application.
• Whether it is fully sealed, since it will be worn against skin for hours.

Small formats designed for this purpose are usually grouped together, which makes comparison straightforward. A category such as the inWonderstate listing states size, sealing and control method per product, which covers three of the four questions above before anything is ordered.

Devices controlled through an application involve an account, a connection and a company holding whatever the application records. Some publish clear policies and some do not, and the category has a history of doing this badly. Anyone uncomfortable with that has a straightforward alternative in a radio remote, which needs no account and no internet connection at all.

Public use is the reason many of these devices exist, and it is worth being clear about the line. Anything that involves people who have not agreed to be involved is not discretion, it is a different matter entirely. Between partners who have agreed, the practical questions are the ordinary ones: does it stay in place, and how loud is it under clothing.