The 37-year-old engineer at the electrical company ERDF was on Tuesday jailed for six months with an 18-month suspended sentence for filming guests in his shower, 20 Minutes reported.
He attracted his guests to his house by placing an ad on the global Couchsurfing website, which allows travellers to stay in hosts' homes for free.
The man admitted to using a hole at the back of his wardrobe to watch female guests while they washed. He also admitted to adding hydrochloric acid to their shower gel to prolong their showers.
“I wanted the girls to shower longer, so they would stay and rub themselves to get the product off,” he told investigators.
The case dates back to July 2012 when a young German tourist accused him of putting the anti-anxiety drug Lexomil on a her slice of bread and butter and putting hydrochloric acid in her shower gel and on her knickers.
The man confessed to having voyeuristic tendencies, which was confirmed in court by a psychiatrist.
However he denied that his actions were sexually motivated.
“What interested me was going out-of-bounds, it wasn't necessarily sexual. It was about seeing without being seen,” he said.
Although he said he had offered his sofa to around 40 mainly young female travellers since 2006, he claims that he only spied on five or six of them.
In 2009 he was also caught trying to photograph a woman in the showers at a swimming pool in Bordeaux.
The German victim's lawyer described the man as “an unremarkable person” who “doesn't seem suspicious”.
“The thing that makes him dangerous is precisely because he doesn't appear to be [suspicious],” she said.
But the man's lawyer pointed out that he did not sexually abuse his victims, remarking that he was “still immature but extremely intelligent”.