The computers do measure altitude (local ambient pressure) as well it just doesn't tell you its doing it.
The old aladins used to have 3 mountains on the screen telling which band you where in.
The normal was 2 mountains worth in an aircraft and only once i got 3 on a 747 going down to south America. We had a theory that a 12 hour flight would give us extra bottom time but it made no difference.
The most likely way your computer is going to get broken is if its in your checked in baggage and it goes into a unheated hold. It freezes and ice crystals form in the LCD display and breaks that.