2. The Alert feat negates surprise
Because the Alert feat (PHB, p. 165) states:
You can't be surprised while you are conscious
A character with the Alert feat cannot be surprised while they are conscious.
"Surprised" has a clear mechanical meaning.
If a character is surprised, they cannot act on their first turn of combat, and after their first turn, they are no longer surprised.
A character with the Alert feat who rolls a low perception check can be unprepared, but never surprised. Perhaps they don't have enough time to wake all their allies before combat starts or they don't have time to get into position or take the action required to don a shield (before combat). But they can never be "surprised".
Rules as Written, critical failures are only for attack rolls.
It is a common house rule that rolling a 1 on a d20 results in a critical fail, whatever the context - but there is no rule in D&D 5e that states that is the case for anything but attack rolls, where the result is simply "you miss".
- The optional rule on page 242 of the DMG ("Critical Success or
Failure") doesn't explicitly state that a 1 rolled on an ability
check overrides a feat's features.
- While it is not called "critical fail" or "critical success" the
death saving throw is a unique case in the rules where the
mechanics of a benefit, or harm, accrues to a saving throw coming up
20 or 1. (On a 20 you have 1 HP and are no longer unconscious, on a
1 you get two fails).