This is a topic that I did not address in the books, but I certainly studied (in fact I studied a lot about the issue because, remember, I’m obsessive :-P).
Some of you will know that the book The 4-hour body from Tim Ferriss (100% recommended by the way) sparked my interest about testosterone, and in that book, Tim Ferriss talks about an interesting self experiment.
He quotes an interesting study and I quote his book:
“Lo and behold, jumping from article to article on Medline, there were more than a handful of studies that showed significant decreases in serum testosterone in rats following even moderate exposure (30 minutes per day, 5 days a week, for 4 weeks) to 900 megahertz radio frequency electro-magnetic fields (EMF), which is what most GSM cell phones produce.”
You know, they are rats and not humans, we tend to jump into conclusions starting from studies that don’t translate well to people, but this is no good. I continue quoting:
“Of the dozens of studies that I found, most done in Europe, more than 70% concluded the same thing: cell phone radiation impairs sperm function.”
As every western person, Tim Ferriss carried his phone in the front pocket, near to his testicles, almost always. What did he do? He tried a little experiment and, for 11 weeks, he decided to keep his phone on the other side of the room. Or, if he had to go somewhere, he strapped it to his arm (with an iPod armband, don’t use duct tape) or in a backpack pocket. He also tried to turn it off if carried in a front pocket.
After 11 weeks these were his results.
Ejaculate volume: 44% increase
Motile sperm per milliliter: 100% increase
Motile sperm per ejaculate: 185% increase
I won’t lie, he says that his experiment is far from perfect, but, you know, I instantly stopped carrying my mobile in my front pocket.
And this is not all, what about wifi, because wifi operates in a similar way than mobile phones.
Well, bad news (as always), take a look at this study where a team of Argentine scientists led by Conrado Avendano of the Nascentis Center for Reproductive Medicine in Cordoba found that placing drops of semen from healthy men under a laptop connected wirelessly to the Internet.
After four hours next to the WiFi-connected computer, 25% of the sperm had stopped moving and nine percent showed DNA damage.
By comparison, semen kept at the same temperature but away from the computer showed just a 14% drop in mobility and only 3% suffered DNA damage.
It’s not the only study that says this kind of things and, I must confess, I’m writing this with my laptop in my lap, frying my little swimmers…
This is fine, but what about testosterone?
Well, you can bet there are no better news.
The Radio Frequency Radiation (RFR) that is considered “dangerous” (by U.S. standards) is considered to be anything above 0.08 W/kg, so wifi levels are below that, but according to, for example, the studies of Navakatikian and Tomashevskaya in 1994 a RFR at low intensities (0.01 – 0.1 mW/cm2; 0.0027- 0.027 W/kg) induced behavioral and endocrine changes in rats. What changes?
Decreases in blood concentrations of testosterone and insulin.
Again, this has not been tested in humans and I’m far from that pseudoscience movement that tends to blame everything that is modern. In fact, there has been a recent meta-study in 2017 about wifi and the like, and it does not seem the root of all evil.
In fact, according to this other study  reviewing other works:
While some animal and human studies revealed alterations in reproductive physiology in both males and females, others did not report any association. The in vitro and in vivo studies to date are highly diverse, very inconsistent in conduct and, in many cases, report different primary outcomes.
In these cases, my take is this: it costs nothing to apply these little tips, especially when you see this other study about erections and cell phone use  that stated:
We found a potential correlation with cell phone usage and a negative impact on EF. Further large–scale studies confirming our initial data and exploring the mechanisms involved in this phenomenon are recommended.
It seems that wifi, smartphones and the like are not the best friends to testosterone. Those things lower our beloved hormone and our beloved sperm, so I’m just going to finish this article and shut down the damn laptop and wifi.
As always it seems that going caveman is the best recipe to regain healthy testosterone levels…
 Challenging cell phone impact on reproduction: A Review Zaher O. Merhi
 Cell phone usage and erectile function. Badereddin Mohamad Al–Ali, Johanna Patzak, Katja Fischereder, Karl Pummer, and Rany Shamloul