I love this film and watch it often! I also have a few CDs of Carthusian chant that are great–slower and more dignified, in a way, than Gregorian chant. The monks also make a Carthusian tea that I buy whenever I get the chance, to help support their life.
One may also ask, if they live by themselve there is no one to contoll them if they are following the monastery rules or not so how do we know if the brothers are following the rules.

A valid question, but think for a minute about how large groups work and you will have your answer. One man might hide a secret, two, with difficulty, but if 30 are in on it, it is no longer a secret. All those monks
joined the monastery in the first place because they believed in the Carthusian vocation and wanted to live that life. Such men, especially the young ones, would be the first to sound the alarm if the ideals of St. Bruno were being violated–and any newcomer interested in taking vows with them would run if the actual discipline were not being kept. Also, monks visit from other monasteries fairly regularly, so that any misbehaviour would quickly be known.
The real kicker, though, in my opinion, is to judge the tree by its fruits and take a look at some of the writings produced by these monks. For example, the Carthisian novice conferences published under the title
The Way of Silent Love, in my opinion, equal the writings of a Doctor of the Church–though since they are published anonymously, only God will know the sanctity of their author.