As you the general public you may see this as a device which has been around for many of years which has never been of any use. If someone in you're house hold, is of any vulnerability please remember it is of use. Vulnerability may consist of letting your teenage child stay in the house alone, mental or physical disabilities or even and old age pensioner. A door viewer can save your vulnerability against opening your door to a stranger who may want to harm you. This simple device does not have to be fitted from a 24hr emergency locksmith but anybody holding little diy knowledge and skills. By having a door viewer you can see who is on the over side of the the door and now you don't have to open the door to see who it is. James is your local friendly locksmith in Cardiff 24 hours a day 
I won't be able to see the person anyway if it is night time
Door viewers are made to take a wide field of view around your front or maybe even back door if wanted to fit to one, By the viewer taking a larger view it is also taking a lot more of the surrounding light around that area which means that the person or object which you are looking at can be made out quite clear. Not a lot of light is needed but the more is obviously better and the moon can have enough sufficient light for the viewer to operate.
Remember if you can't see or make out the object person don't open the door under no circumstances they might be holding there finger or hand over the viewer to stop your access of seeing them.
If you have frosted Glass as a window in your door a Door Viewer is still necessary as you will not be able to make out the person at the door. Even if they have seen your shadow through the glass remember you haven't lost your vulnerability as you haven't opened the door.
If you need a assessment of your home security or you think some of your security can be updated then give your local professional locksmith a call James Locksmith Cardiff 07967725135
After our locksmith in Cardiff have finished the installation of your Van Deadlocks it is very important that you the customer and any employees get in to the habit of actually locking the van. As the lock is new it is sometimes difficult to get in to the habit of actually locking the newly fitted lock. You Must Get Into The Habit, It keeps your valuables Safe. Our Cardiff Locksmith will stress to you how important this is to lock and how to check it is locked.