‘how much gas does my oven consume’? As relatively few activities in the
home run on gas as compared to electricity, it’s possible for users to make
some rough guesses from the data. For example, if no one is at home but gas is
being consumed, that might mean that the heating is on (and thus that the
schedule should be changed). But for more detailed insights, the system would
need to analyze longer-term patterns in gas consumption data and estimate
likely usage by appliance.
When it’s not possible for all system data to be perfectly synchronized or
‘live’, it’s important to indicate how old data or status information may be. For
example, you might show a timestamp for a sensor reading, or the time that the
latest status information was received.
In the energy monitoring example above, it’s important that users understand
that the two energy readings are not equally ‘live’. You could display a
timestamp for each reading, but you might also choose to display information
in a different format. You might use a line graph for electricity (because you
have near continuous readings) but a bar chart for gas, where readings are only
intermittent. (See e.g. figure 9. 32 ).
Figure 9.32: gas vs electricity displays showing timestamps. (mock up)
It’s important to ensure that system status information is as accurate as it needs
to be for the context of use. In a safety critical system, it should be clear when
data may be out of date or an instruction may not yet have been received or
acted on. A remote door locking system should not pretend that it has locked
the door until proven otherwise! Perhaps the biggest challenge design-wise is
how to design these behaviors for a system that needs to do multiple things
with different responsiveness demands, such as heating, lighting and safety
alarms. It’s safest to err on the side of communicating what is actually
happening, but in some circumstances that may feel inelegant.
Handling cross-device interactions and task
migration
Cross-device interactions require users to switch between devices in order to
achieve a goal. Examples might include syncing data from a wearable fitness
tracker to a smartphone, or connecting home sensors to a gateway.
Transitions between devices should be smooth and well-signposted. The word
‘seamless’ is often used in cross-platform UX, but it’s probably misleading.