Slice the carrot, daikon radish, cucumber, and jalapeno into matchsticks or disks/rings.
Add all vegetables into a quart-sized mason jar and a pint-sized mason jar (or two quart-sized jars).
Add water, apple cider vinegar, and salt to a small saucepan over medium-high heat.
Bring the vinegar mixture to a boil. As soon as it starts boiling, stir the mixture, remove it from the heat, and pour it into the jars over the vegetables. This is obviously a hot pot pouring hot liquid so be careful. I typically do the pouring process in the sink so any spilled near-boiling liquid does not hurt anyone.
Close the jar lid and let it rest on your counter until cool.
Add to the fridge and enjoy some great pickled veggies over the next few weeks.