My Google Cardboard (v1) has a magnetic button.
With the Google Cardboard app, the demos were really annoying since ''pressing'' the magnetic button was not reliably detected. Furthermore: GvrView no longer supports magnet trigger detection or NFC-based pairing for v1 Cardboard viewers. (release notes)
A solution was required. Buying a Google Cardboard v2 with a conductive foam button? Cool stuff, but I wanted a working button with the Google Cardboard v1.
My clothespin + aluminum fix works for me. By the way, I have a capacitive touchscreen.
The button is in the field of view, but it is not disturbing in the VR experience. I've chosen the lower right corner as button position, because: 1) I am a right-handed person and 2) having in mind Web/GUI-design, the user pays less attention to the lower part of the website or GUI (Gutenberg diagram: Gutenberg diagram).
You need: a really small piece of cardboard, aluminum foil, a toothpick, tape, a clothespin, a scalpel knife and a hot-melt gun or another type of glue.
Step 1: Take Apart the Clothespin. You Need the Spring.
Step 2: Take the Google Cardboard
Take the Google Cardboard. On the bottom of the Google Cardboard cut out (with the scalpel knife) a rectangle the size of the spring (also a little bit larger is good, less stable but easier in button usage). I have chosen the bottom-right of the Google Cardboard, but you can take any position where the spring reaches the touchscreen. In my case, I use the button with my right thumb. The top of the spring, which is extended with the small piece of cardboard, reaches the touchscreen, but does not trigger the phone's menu.
Step 3: Take the Small Piece of Cardboard
Take the small piece of cardboard, which was cut out of the Google Cardboard previously. Glue it (with the hot-melt gun) to the top of the spring.
Take the aluminum foil. Fold it in a way so that you can wrap the folded aluminum foil around the cardboard onto the spring. Apply a last small drop of glue to fix the wrapped aluminum foil.
Step 4: Reassemble
Put the spring in the hole you made before in the Google Cardboard. Insert the toothpick into the hole of the spring so that it works like an axis (I cut the left and right side of the toothpick a bit to shorten it). Fix the toothpick with some tape on the left and right side.