👁 Image Non-negotiable blocks in probably any sane double door. The symbolic glass blocks represent 12 blocks that must be empty of solid materials. The stone blocks represent 4 blocks that must be solid. This has to do with requirements #4 and #8.
Doors are a simple thing to automate. The challenge grows when you add requirements like:
1. Must allow a ridden horse
2. Must stop a riderless horse
3. Must stop most mobs
Tripwire-based designs usually can't stop zombie horsemen, skeletal horsemen, frogs, bees, allays or parrots, so those are acceptable
4. Must stop baby zombies and small pets like foxes and ocelots which can get through redstone wiring spaces
This means that the doors must be flanked by solid blocks at least 2 blocks high, and tripwire-based designs must take additional care not to create a staircase that lets a small mob (or a piglin crossbowman for that matter) climb to the tripwire level
5. Must be easy to operate by a horseless player (specifically, no need to aim at any button or similar small target when just passing through)
6. Must be able to latch the doors open for an extended time, in case the player wants to lead many entities through
(6a) Optional: any lever should be at eye-height or higher, because that is convenient for mounted players, and because a lever near the ground prevents placing carpet or other decorations.
7. Must support iron doors - or technically, some mechanism that is not wooden or copper doors
8. Doors should be flush with the blocks flanking it, to prevent the minor annoyance of running into the hitbox of an open door. See picture.
(9) Optional: be builder-friendly, i.e. a design that can blend into a lot of different builds. Like by not mandating too many specific blocks near the doors and permitting things like carpet on the ground instead of redstone dust.
Tripwires are an obvious choice (even for horseless players, who can simply jump into the tripwire, satisfying requirement #5), but it is possible to use creakings or sculk sensors as well.
The innovation here is that three separate shriekers help the door stay open while the player is hanging around nearby, without "flickering closed-and-then-open-again", since their 4.5-second durations are unlikely to fire simultaneously. The calibrated sculk sensors also help there because of the 10gt reset time instead of sculk sensor's 30 gt, which makes the door more responsive.
Wool or carpets can be added to control the zone of activation.
A lever can be added underneath one of the blocks with offline redstone wire, near the torch. The block must be opaque then.
