Lock plastic windows from children for 92 rubles with their own hands

We all have children, in the life of parents nothing can be more expensive than the safety of our own child. I faced a task: to install locks on plastic windows, the price of the cheapest option I found on the Internet is 600 rubles, I need to block 4 windows, total 2400 rubles. I think the price is unreasonably high, after reflection, a brilliant idea came to me. So let's get started.
Objective: to install a lock on the window for a price that is at least 2 times less than what is offered on the Internet for a turnkey solution, while not losing quality and reliability.
Decision:
1. Buying the right materials.
2. Installation.

Materials purchase

Let's move on to point 1, we need one window:

1. two metal corners;
2. four screws, 16 mm long;
3. braided metal cable with a diameter of 3 mm, length 20 cm;
4. cable clip.

I went to a large, notorious hardware store, decorated in green colors (everyone understands that this is not an advertisement). And I got there:

• corners metal white 4 pieces. for 48 rubles;
• screws 40 pcs. for 55 rubles;
• metal polymer cable 10 meters, diameter 3 mm for 102 rubles;
• cable clamps 2 pcs. for 122 rubles;

acquired in such quantity since don't sell less. All materials are shown in Figure 1.
We proceed to step 2 of the installation, for this we need the following tool:
1) A screwdriver or Phillips screwdriver;
2) A screwdriver with a 7 mm head or a 7 wrench.
The tool is shown in Figure 2.

Making a plastic window lock from children

We proceed directly to the installation:
1. First we fasten the corners to the casement windows using self-tapping screws as shown in figures 3 and 4.
2. Next, we thread the cable through the holes of the corners, choosing the desired length so that the window can open for ventilation.
3. Using a clamp and a screwdriver, fasten the two ends of the cable.
Everything, the lock on the window is ready. Figure 6 shows the installation of the corners on two movable leaves; Figures 7, 8 show the option of fixing the corners when only one movable shutter is required to be locked. The cable can withstand tensile stress of 220 kg, this is quite enough for a child.

Cost summary

As a result, I spent 92 rubles 54 kopecks on locking one window:

• 48/2 = 24 rubles for two corners;
• 55/10 = 5.5 rubles for 4 screws;
• (102/1000) * 20 = 2.04 rubles per 20 cm of cable;
• 122/2 = 61 rubles per 1 clip.

My benefit was 600 rubles. - 92.54 rubles = 507.46 rubles, or (600 / 92.54) * 100 = 648%.
I consider the task to be completed perfectly!