Much of security is about making it difficult for a burglar to break in… the more barriers there are, the slower the burglar can gain entry and the longer he (or she) is kept outside and possibly visible to neighbours… or be more likely to make a noise and alert the homeowner or their dogs.

The beauty of this idea is that through it works in very much the same way as the purpose-made door chains you can buy at Mica – and those door chains are very good at what they do – this setup allows you to set the gap as you desire.

Having said that, always remember NO security system or measure is foolproof; this one simply adds one more layer to your security measures, but nothing beats being vigilant, thinking around corners


  • Welded steel chain – 30mm – length of about 300mm or so.
  • Round saddle clips – standard size – 2
  • 8 gauge 30mm securing screws – 4
  • One padlock


  1. This pair of French doors was required to be allowed to be kept ajar to allow a cooling breeze on hot days… but how could it be secured to allow cool air and perhaps Purrsie in – but keep intruders out? It is simpler than you think, as it turns out…
  2. Using a hacksaw or as in this case, a bolt cutter, snip off a 300mm length of the chain.
    Note 1: Use welded chain and not the much thinner, more decorative non-welded versions. They are designed for lighter use… for supporting pot plants or downward opening cupboard drawers, for example, and their links are not welded and could be pulled apart with a sharp, forceful tug – or push against the door, or prised apart with a screwdriver without too much effort.
    Note 2: Do not make the chain too long in case you one day set the gap so wide that an intruder or his or her little sidekick could squeeze through and open a backdoor, for example.
    Note 3: This sounds obvious, but do not leave the key in the padlock or in any position where it is visible from the outside… for obvious reasons!

  3. Here is the chain with one saddle clip on its end link.
  4. The chain is attached to what will usually be the stationary, fixed door, with the second saddle clip attached to the second door to be swung ajar.
    Hint 1: As an alternative to the screws used here, you can use mirror screws. Once the screws are tight, apply string adhesive to their heads and screw on the chromed dome heads, securing them tightly – now no screwdriver can be used from the outside remove the saddle clip.
    Hint 2: Alternatively, once the screws are secured, push a small amount of epoxy over each head, smoothing and doming its surface so that it is more difficult to apply a screwdriver from outside.

  5. The completed setup… the beauty of this is that you can adjust the gap you wish to allow depending on where you secure the end of the chain with the padlock. At the very end you will allow the largest gap. Secure the chain at any other point along its length and you will be able to set the smaller gap to whatever you like.

Project guide

Skill level: 1

Estimated time: 30 minutes at the most.

Cost: <R100 or so

Assistant: No

Tools required:

Drill/driver, hacksaw or bolt cutter.


These materials are available at Selected Mica Stores. To find your closest Mica and whether or not they stock the items required, please go to, find your store and call them. If your local Mica does not stock exactly what you need they will be able to order it for you or suggest an alternative product or a reputable source.