A pomodoro timer that somebody else can see
A pomodoro on your own is a suggestion. The timer has no opinion about whether you start it again after the break, and neither does anyone else.
Nothing enforces the next one
The technique is sound and the failure is never the technique. It is the fourth break turning into the end of the afternoon, with no cost to skipping the restart because nobody was waiting for it.
A timer only you can see is a plan. A timer somebody else is also inside is an appointment.
The same technique, with a witness
Everything about a pomodoro, except that starting and stopping are not private.
Not two timers you started at roughly the same moment. The same countdown, and it reads the same on both screens.
Either of you can pause and it stops for both. Which means stopping early is a thing you did, not a thing you got away with.
The classic 25 is there, so are 50 and 90, and so is any number you type. Some work does not fit a tomato.
Three steps, then it is a habit
One of you sets it. Both of you are in it from the moment it starts.
The clock counts on both screens. A pause from either side stops it for both.
Then start the next one, because the other person is still there waiting to.
The break is the part worth sharing
A round of something takes about as long as a short break and is a better reason to come back than a notification telling you to.