PDA
The PDA is waterproof and can even accompany Lara on her long journeys through water.
From the Official Site
While Lara's headset keeps her in contact with her support team, her PDA is her field workspace. It stores and organizes notes on short term goals as well as useful data on gear, weapons, and progress. Its versatility is matches only by its sturdy construction - enough to withstand the abuse one might expect from accompanying Lara to the most dangerous places on Earth - and it's waterproof, too.
Underworld
Lara carries it in Tomb Raider Underworld as well. It now includes an active sonar map; a revolutionary new tool that emits a sonar ping to create a 3D image of Lara's surroundings, perfect for uncovering hidden items and locations. [1]
Description from PDA in Tomb Raider Underworld
As the latest generation of Personal Data Assistants, this device can perform various tasks necessary when "in the wild" including a sonar mapping module designed to create a low resolution 3D maps of the surroundings, a data archive and reference retrieval library, and long-range satellite communications.
- ↑ Fact Sheet by Eidos