The contraceptive plaster (EVRA, for example) causes the hormones oestrogen and progestogeni to be secreted, which are absorbed in the blood via the skin.
You stick a new plaster on your skin every week for three weeks. This is followed by a plaster-free week.
The chances of pregnancy are approximately 0.3% per year. The plaster is not reliable in women who are overweight. For information on how to use a contraceptive plaster, go to https://www.thuisarts.nl/contraceptiveplaster/I-want-to-use-a-contraceptive-plaster