When we removed the external part with the keypad attached, which was at the lower part of the main body, we immediately noticed the waterproofing mechanism.

Under the external part was a soft plastic cover, which was tightly sealing the space inside the chassis where the boards and other components were contained. The peripheral part of the cover was convexed so as to be tightly fitted in the recessed groove on the chassis side. It looked like a plastic food container in the kitchen.

It should be noted that the upper part of the main body incorporating an LCD panel also had a similar watertight structure, although this article only discusses the lower part.

We found a hole formed on the cover sealing the lower part of the main body. It was for a microphone at the upper left. The hole was covered with a convex part on the back side of the external part with the keypad attached. This seemed to be an effort to improve the sound collection effect of the microphone.

Because the interior part of the chassis was covered, the circuitry of the keypad is also under the cover. When the user presses a key, a switch in the circuit block is pushed via the cover. The circuit block had LEDs used as backlights for the keypad.

The cover had a white area at the position below the keypad, etc, probably to diffuse the LED light. The portions above the LEDs were painted black. The manufacturer likely designed it this way so that the LED light would not appear as spotty.