Probably the safest ...

There are, to my knowledge, to secure four ways sockets in front of children. The most common is probably the rotary contact protection for gluing. Not very safe because the things eventually fall out of the can
The second option is directly secured sockets. But this is expensive and relatively complex since the entire box needs to be changed.
You can also use canned locks. These then block but the socket and must be removed. This creates the danger that a child pulling a plug out of the socket and then has free access.

In this version, we combine the advantages of other systems. It is easy to retrofit by doses fixing screw in the middle. This also prevents the protection is released from the socket. It must both contacts are pushed evenly up to gain access to the box. This jump when removing a plug back and seal the can. In addition, this kind of protection is very low, if not, as required by Pearl, such a high shipping.
By itself, this system thus combines all the advantages of the other systems without considering their disadvantages. However, there is a negative point here. The return springs do not seem to sit 100% in each part. So do not grab all the protectors on their own back! This is a huge shortcoming what this part costs two star. Removing the plug itself can advance with the contacts the bolt again. Removes a child a plug it is the certainly do not. Here, then, is essential to ensure it before buying

Conclusion: The best protection offers definitely already in the factory-backed socket. Who but no money or do not feel like sharing that finds here a convenient and fast alternative to verbauende. However, even at the expense of safety ...