At many companies, employees take a laptop to/from work every day.
In the past, laptops were heavy enough that it would be incredibly obvious whether a laptop was in a bag or not.
Modern laptops are light enough that it is possible to take a laptop bag (Figure 1) to work without realizing that there is no laptop inside. This can be an annoying and time-consuming mistake.
Proposed here is a laptop bag that makes it unavoidably obvious that there is no laptop inside. The model shown in Figure 2 pops up a spring-powered flag whenever a laptop is not present.
The flag-based approach described above makes it incredibly obvious if a laptop is not present. It also has the advantage of being easily overridden by a user who is intentionally not packing their laptop: they can simply press down on the flag while zipping the bag’s laptop compartment.
Rejected simpler Idea:
One could imagine a laptop bag with a transparent panel that would allow visual confirmation of the presence/absence of a laptop. Although this would work (and requires no moving parts), it would still be easy to grab the bag in a rush without realizing that the laptop was missing. Additionally, it has the disadvantage of advertising the presence of a (highly-stealable) laptop to fellow commuters.
Tactile alternative to the “flag” idea:
For a briefcase, the handle could change texture when the laptop is present. For example, dozens of metal spikes could protrude from the handle until a laptop weighed down the laptop cradle, at which point the spikes would retract into the handle, like they were part of some kind of Indiana-Jones-style ancient temple trap. (This could be all done mechanically, with no need for electronics, using cables that connected the handle to the laptop cradle.)
You should crowdfund a laptop bag like this right now! If you are successful, it will prove that a market exists, and hundreds of much-cheaper knockoffs will flood the market before your initial prototypes are even done!
PROS: Never forget your laptop again!
CONS: Any object that is similar in shape to a notebook computer (e.g. an actual notebook) would cause false positives.