Keep your headphones off of your lap:

Testicular zap ‘may stop sperm’
bbc.co.uk

A dose of ultrasound to the testicles can stop the production of sperm, according to researchers investigating a new form of contraception.

A study on rats published in Reproductive Biology and Endocrinology showed that sound waves could be used to reduce sperm counts to levels that would cause infertility in humans.

Researchers described ultrasound as a “promising candidate” in contraception.