do you have to wear both of them at the same time?
CHRIS K Yes, and you do not want to take them off at all. I had a dive master tell me he personally has seen some effectiveness with them, but you must leave them on even during your dive.
CHRISTOPHER R I find that if you only wear one, that sometimes it is effective; however if you wear both then you get twice the nerve stimulation to make it work better. It is all about nerve stimulation and each person is different so you will only know if you try.
JOHN D I have not had to, but they've worked better for me when I did. It's probably because they can shift their position as you work and wearing 2 keeps the pressure point depressed more reliably.
LISA A Yes you need to wear both to be effective. Sea-Band website has an illustration on where to place on wrist.