Earlier quoted context omitted.
> F105W which is basically the same watch with a vastly improved backlight Can’t stress this enough. The F-91W is useless at night because the backlight brightness is terrible. The F105W has an indiglo-style “EL” light that is very effective. The two watches are nearly identical from an aesthetic perspective. The functions are identical as are the buttons.
Indiglo has good looks and function. What I dislike is that it requires a high-voltage driver. As tiny and low-current as that may be, it is electrically and even slightly acoustically noisy, and not something that belongs in a low-voltage wristwatch.
But in either case, it's perfectly safe. There's no way to touch either the hot parts or the high-voltage parts. And even if there was, the battery doesn't have enough oomph to do anything more than tingle once the prickly part was trying to drive something as massive as a fingertip.
I noticed the noise too, when I owned one, but I figure silencing it would've cost size, weight, and power. And the noise was never more than a curiosity, so I'll take it!