With the flip of two switches, men could one day curb their sperm flow and activate easily reversible birth control, according to ballsy German inventor Clemens Bimek.

Bimek, a carpenter who was frustrated with the lack of male-controlled contraceptives, came up with the idea after watching a television show about anatomy. Determined that his sperm shut-off method would work, the spunky creator patented the idea in 2000 and tested it out on himself (in collaboration with a surgeon) in 2009—and so far so good, he reports. Bimek intends to organize a 25-person clinical trial this year of the method, called the Bimek SLV.

The Bimek SLV works by implanting two devices—shut-off valves—in the scrotum. The valves are each "as small as a gummy bear," according to advertisements, and made of non-magnetic metallic components and a biocompatible polymer already used in medical implants. The devices get attached to the vas deferentia, the two ducts that transfer sperm from the testicles to the urethra. During implantation, each vas deferens is cut and the ends are plugged into the in and out tubes of a valve.

After the implantation, the valves’ switches can be flipped by simply pushing on them through the skin. In the off position, sperm are diverted out of the ducts and dumped back into scrotal tissue where they would theoretically be reabsorbed by the body.

Bimek estimates that the total cost of the surgery and the devices will be around $5,426 (€5,000).

Switching from on to off doesn’t produce immediate results, however. The lines have to basically be flushed of swimmers to avoid pregnancy. Bimek estimates that this would take about 30 ejaculations, or about a month. Thus, the method will not work as “emergency” contraception. Also, it wouldn’t prevent the spread of sexually transmitted infections, such as unstoppable gonorrhea.

To reopen the valves, a user will have to hold down a separate safety button to flip the switch back. This ensures no accidental switching.

In interviews with German magazine, Der Spiegel, doctors expressed some concerns about the implants, including scar tissue that could develop around the valve and make the switch hard to flip. Also, there is some concern that the valve could clog with sperm if left in the open position for long periods of time. Such clogging might require periodic doctor’s visits for line-clearing, which may be unpleasant.

Last year, a urologist from Munich, Dr. H.W. Bauer, signed up to support the trial and the development of the implants. Bimek is now crowdsourcing funding for the trial and recruiting volunteers.