8.3.3 The initial connection
An important consideration is when a product should be allowed to attempt to make a pairing. This is not always obvious and varies between devices. For consumer devices, it may be a process that is initiated the first time a device is turned on, or when a battery is inserted. It may also be initiated by a specific ‘pairing’ switch, or an action on the user interface. Unless a specific filter ensures that only appropriate devices will respond, it implies a second user interaction that will select the correct device after a list of devices within range has been presented.
A first rule of thumb in designing the user interface is to apply Intelligent filtering and only display those devices to which it makes sense to connect. For a ZigBee network, it probably doesn’t make sense to display thermostats when commissioning light switches. Nor does it make sense for a Bluetooth printer to detect and display keyboards. The concept of wireless connectivity is still alien to most users: displaying irrelevant possibilities will only confuse. The endpoint device ID in ZigBee and the device icon in Bluetooth, if used sensibly, can help designers to make sense of the multitude of connection possibilities in their user interfaces.
It is possible to configure most wireless products so that an action is required at both ends of the link to initiate a connection. This is generally a sensible approach, as it protects against unauthorised devices trying to make connections. When implementing schemes like this, bear in mind that they are generally proprietary applications that you have built on top of a standard, so may appear inconsistent to a user. The manufacturers of devices you may want to interoperate with will probably have made different choices. Don’t do something different from the rest of the industry without good reason, as differing interfaces will confuse the user. Don’t underestimate the power of what they have already learnt. One of the simplest techniques is to have a ‘connect’ button on both devices. When both buttons are pushed at the same time, the devices connect. Even this is moderately counterintuitive to most users, and rarely works between devices from different vendors. The more complex connection schemes that are frequently employed often seem designed to create a support call. Whatever scheme you choose, test it on potential customers at an early stage of the design process. A good example of an attempt to standardise the simple button approach is the wireless protected set-up specification from the Wi-Fi Alliance.
The more that can be done to remove decisions from the user during the connection process, the better. However, in achieving this, there is a potential trade-off in usability and security, so these
should be considered as part of the connection interface design.