I recently bought a holster type case for my work phone which would lock the phone when it was put in the case. I used that for a while and then thought a flip case would be better so got one for a stupidly low price (99p inc p&p) from AWKIAS. However, this one didn't lock the phone when shut and my phone would occasionally make calls to random people in my address book. So I thought I'd remedy the situation . . .
(This is one of those Instructables where the writeup takes many times longer than actually doing the thing!)
Step 1: Tools and materials
To do this mod you will need a sharp scalpel or craft knife, a non-metallic prodding device (a coffee stirrer or similar) and some adhesive; Either cyanoacrylate (superglue) or general purpose will do.
You will also need a small magnet, not more than a couple of mm (1/8") thick. The one I used was from a broken brushless motor, but any source will do, including stick-on magnetic rubber etc.
Step 2: Finding the sweet spot
With a bit of experimentation sliding the phone in and out, I discovered that the holster had a magnet embedded in the case around half way down which activates the 'lock' sensor on the phone. Other phones may be different, but by sliding a magnet over the front of the phone you should be able to find the right point.
Once you've found the approximate area, move the magnet with the non-metallic prodder to find the centre of where it operates. We now have to mark this point on the case flip-lid.
Rather than pressing the case shut and looking for the indentation, I put a tiny drop of water on the magnet then closed the case. When I opened the lid I could see where the magnet had been by the darkening of the fabric.
Step 3: Embedding the magnet
With the scalpel, cut out the outline of the magnet into the case lid. Make the first cut quite shallow and ease the blade underneath so you can lift out the top square with the fabric to replace later. Then cut around and lift out enough layers to bury the magnet and leave the top layer flush with the case lid.
Add a bit of adhesive to the bottom of the cutout, insert the magnet and carefully put the top layer back in place with another drop of glue. If you've done this carefully the modification should be almost invisible.
Step 4: The finished result
To test the mod, make sure there's no excess glue going to mark the screen, then close the cover and your phone screen should turn off. To fully test the locking, manually lock it while open, close the lid and then open again. The phone should unlock and be ready for use.
N.B. The magnet will interfere with any compass based app you may use as the magnet's effect is many times that of the Earth's magnetic field on the compass sensor. However, this will be true of any phone case which uses a magnet to lock. If you need the compass to work, take the phone out of the case.