Thinner (less durable, but who cares?) plastic shell to free up space for explosives, but would likely be obvious if someone opened it - which might be a common thing if these were being used as remote triggering devices.

If they were using a AA battery, replace the battery with something that provides you space to work (e.g. put in a AAAA or button cell that would provide appropriate power but lower capacity) because you don't really care if the battery life drops from months to weeks.