The "armbands " you are referring to are called Sea Bands. They are elastic bands with tiny built in bumps that are worn on the wrist with the bumps placing pressure on your pulse points. They are sold wherever travellers remedies are sold, such as major chain pharmacies. They are about $6 or $7. Do they work? Two of my grandchildren wear them after demonstrating signs of car sickness (all over the back of the car). There is a physical effect , and a psycological one as well. They have been around for years and users swear by them. There are no side effects.
Other remedies include Dramamine and Bonine. These are mosr effective when taken before getting motion sick. One remedy that supposedly works after getting sick is the common antihistamine Benadryl. It is apparently an effective anti nausient as well. Another suggested remedy is to use pure ginger.