At the beginning of an encounter, the DM determines which participants are surprised, then participants roll initiative.
A feat like Alert allows a character to never be surprised while conscious.
There are a variety of non-action, non-movement activities that can be taken during a turn. Here are a few examples of the sorts of thing you can do in tandem with movement and action:
- make “utterances and gestures”
- draw or sheathe a sword
- open or close a door
- withdraw a potion from your Backpack
- pick up a dropped axe
- take a bauble from a table
- remove a ring from your finger
- stuff some food into your mouth
- plant a banner in the ground
- fish a few coins from your belt pouch
- drink all the ale in a flagon
- throw a lever or a switch
- pull a torch from a sconce
- take a book from a shelf you can reach
- extinguish a small flame
- don a mask
- pull the hood of your cloak up and over your head
- put your ear to a door
- kick a small stone
- turn a key in a lock
- tap the floor with a 10-foot pole
- hand an item to another character
Presumably an unsurprised participant could use their action, movement, or activities to do something to try to help the other participants escape their surprise.
Is there any mechanic to remove surprise from other participants in an encounter?