A bath for your testicles has won a James Dyson award, an international award that celebrates design and engineering, and will go through to the final international stage of the competition.

Created by German design graduate Rebecca Weiss, the device named "Coso" is described as an "ultrasound-based, reversible and hormone-free male contraceptive device for home use". The idea is that the user spreads their legs, takes their testicles and places them inside the sleek-looking device, after filling it with water and heating it to the required temperature. The testicles are then hit with ultrasound for several minutes, in order to suppress spermatogenesis.

Essentially, you teabag your way to (temporary) infertility.

"About a year ago I was diagnosed with cancer precursor cervix due to contraception with the pill," Weiss told the Dyson Awards. "After that, hormonal contraception was no longer an option. When my partner and I were looking for an alternative method, we became aware of the lack of male contraceptives.

"The problem is not unique to me personally. It affects many others as well. This is also evident in the current growing public discussion about the lack of contraceptive alternatives. So I decided to deal with the development of a new contraceptive approach for men in my master thesis in Industrial Design at the Technical University in Munich."

Weiss worked with young males in design workshops, to figure out what they would want from such a device, as well as to help figure out the testicle ergonomics. Winning the German James Dyson award, she now plans to test the feasibility of the device, as well as raise funds for clinical trials. 

The idea of using ultrasound as a form of contraception has not come from nowhere; it actually dates back decades. In 1977, a team looked at using ultrasound to the testicles as a contraceptive on cats, dogs, monkeys, and humans. "In all treated animals as well as in human patients the results indicate that ultrasound significantly suppresses spermatogenesis according to the dosage and frequency of treatment, without any effect on Leydig cells or blood testosterone levels," the study found.

More recent studies have found that the treatment may be viable, though a challenge would be getting men to do their bit and attend contraceptive appointments that women have had to for many years.

"Ideally a method should be highly effective after one visit, because many people may not come back for the second treatment," noted Jeff Spieler of the Office of Population and Reproductive Health, Bureau for Global Health at the US Agency for International Development, at the time.

The device, though in early stages, has the advantage of convenience: you can teabag your chargeable device in the comfort of your own home. The device will now face off against other countries' winners, including power-generating clothes and a speech-recognition system that presents subtitles for the deaf and hard of hearing.