Dehydrator plugs are used to prevent corrosion inside an aircraft engine while the engine is in storage. The dehydrator plugs are filled with silica gel that changes color when moisture is absorbed.
Some dehydrator plugs can be reactivated by heating the the silica gel.
If you are not flying for a long period of time these smart plugs will prevent damage from internal engine corrosion. An inexpensive investment since moisture inside an engine cause some serious damage.
Priced around $5 - $10 each.