TL;DR you get a 20 frame tech window from your digital trigger press onwards, but only if it's been 40 frames since the last one.

Frame Data

Two relevant variables

Teching in SSBM depends on the values two variables: timer_LR and since_rapid_lr.

Both values initialise to -1 at game start. They change when you input a digital trigger press.

timer_LR:

  • sets to 0 on any digital trigger press.

  • increments every frame unless it is equal to -1.

  • naturally overflows from 127 to -128 when incrementing.

since_rapid_lr:

  • records the exact value of timer_LR at the last digital trigger press.

  • does not increment, is not a timer.

What are Windows and Lockouts?

tech windows and tech lockouts are purely conceptual:

the tech window corresponds to the period of time where timer_LR is counting up from 0 to 19 and since_rapid_lr is not between 0 and 39.
the tech lockout is simply whenever both timer_LR and since_rapid_lr are between 0 and 39, as another trigger input will extend your time in this state with timer_LR reset, counting up from 0.

Basically the tech window is just:

The 20 frames from your last digital trigger press, as long as you didn't press it for at least 40 frames since the last one.

When precisely do techs happen?

Put simply, you will tech if:

while in the tech window, and while getting launched, you collide with a solid object.

Hitlag

If you're in hitlag, you cannot floor tech. walls and ceilings only.

If a digital trigger press occurs during hitlag, the game will act as if a press happens on every frame from then until hitlag ends. This will put you in the lockout if you're still in hitlag the frame after your trigger press.

Practical Tips

Timing your Tech Input

You have a whole 20 frames before you (expect to) collide with something in which to input a tech. That's a third of a second, which may as well be a month in melee terms.

Press the trigger super early so you can move on and think about what you're doing next. The earlier you input tech, the earlier the lockout timer ends and you can hit tech again.

Fun fact: with perfect timing you can tech twice within 21 frames this way.

Choosing the Tech Type

The type of tech (tech in place or roll in/away, walljump or fall) depends on your inputs at the time when the tech actually happens.

If you're holding a direction when you tech, you'll go that direction.

You can hold it in advance, but you don't need to if you're trying to wiggle out of tumble or SDI or something first.

Tech walljumps with X/Y don't seem to have a buffer or let you just hold the button iirc (I should test this. you should test this)

Hitlag, and More Hitlag

Hitlag techs are often the only way to survive when you get hit while recovering.

If you want to get a tech from hitlag, you really need to hit tech before the hitlag happens.

Sure, you can theoretically input a tech on the same frame that you (A)SDI into the stage wall, but why would you choose 1 possible frame over up to 20?

You still have tons of time

Having to tech before you're hit might make feel pressured to hit the trigger right before you get hit. Don't do this.

Input tech early, even for hitlag techs. You've still got plenty of time.

Hitlag is usually pretty short, like less than 8 frames, so don't wait until right before the hitlag starts and risk getting yourself locked out of tech by the trigger spam game logic.

Even a ganon stomp dair with 15 frames of hitlag still gives you 5 frames before the stomp to input a tech that lasts for the whole window (4 if you need that ASDI motion). Plus, that's only to ensure your tech in the case where you only SDI to the stage at the very end of the hitlag. If you input tech a little too early, you'll likely still have a good portion of the hitlag within which to SDI to the stage wall and then tech.

If you can predict when you'll get hit, and you know how many SDI inputs you need, then you only need to input tech with enough time to get hit and SDI to the wall.

Stay close to the wall

If you're already hugging the wall when you get hit, then you just need to tap in once, regardless of how much hitlag you're gonna be in. Also, if you do make the tech window last till the end of hitlag, then you'll tech from ASDI just by holding in on either stick.

Fun fact: this is a relatively rare case where you can change state while in hitlag. You can still be in hitlag for ages, stuck at frame minus 2 billion (INT_MIN) of the PassiveWall animation. The useful takeaway is that you have until hitlag ends to decide whether you're walljumping.

There is no random motion

While it looks like your character is wiggling about a ton during hitlag, your environmental collision box doesn't actually move on its own at all until hitlag ends. You're only gonna tech during hitlag if you SDI your way there.

Teching isn't always easy, but it's definitely easier when you know how it works. Knowledge isn't everything, though. Take this knowledge to the training lab, and bake it into your muscle memory.

Go forth and tech until the timer runs out. Match into your worst enemy on unranked, and laugh. They have to work so much harder to take your stocks from now on.