All of Apple's MacBook models contain moisture sensors that tell Apple Geniuses whether the laptop has been the victim of a liquid related incident. It seems that Apple is keen to ensure that no water damaged Retina MacBook Pro slips through the net when users bring them in for repair by adding extra sensors into its new device.
If a moisture sensor indicates to an Apple Genius that the MacBook owner has spilt something on the laptop or dropped it in the bath, it could mean that warranty coverage is denied and the owner will have to cough up for the repairs. The MacBook Pro and MacBook Air have eight moisture sensors each, but Apple's new MacBook Pro with Retina display has ten. The new MacBook is more expensive to repair, which is likely to be the reason Apple wants to crack down on warranties.
Hardmac, which discovered the extra measures put in by Apple, warns that checking the moisture sensors is one of the first jobs Apple technicians do when getting a device in for repair, so users should be careful when using their device around liquids. The report also points out that the Retina MacBook Pro's internal design will allow liquid to spread to several components quickly.
Apple says that the moisture sensors only detect when they have been in direct contact with liquid, so temperature and humidity will not affect them.