Status indicator that doesn't use power?

[ataradov]

AndyC_772 suggested it in a post #10.

There seem to be no LCDs like this (single big segment) on the market, so it would have to be custom made.

[brichards42]

Why isn't anyone suggesting a very small lcd display with a few segments? Make it transflexive and you don't even need backlight... and you'd probably only need to pulse it once every few seconds to keep the liquid cristal working.

I think a small lcd display would be good choice if you are using a mcu with enough pins to drive it and it doesn't need to be noticeable at any distance.

[DavidKo]

What about using the LCD (maybe even dot matrix), but to hide for example red sticker behind it. When you turn off the power supply, than it will not be hiding the thing behind it. Also you can use 7seg LCD with reversed polarizer (numbers will be transparent for the active segments with black surrounding) and turn on the 1 and have green background. Such a approach will work even without battery, but will have higher power consumption with good battery.

Other thing what I have met, is used in smoke detector (Hütermann F9), which beeps once every 43s, when the battery is low.

[DavidAlfa]

There're single-pixel lcds for soldering equipment:

www.aliexpress.com/item/1005002280725964.html

However the polarity might be reversed to what you need.

[Psi]

Maybe one of these ~$2 linear actuators with the arm connected to something that shows the low battery message. OR maybe even use it like a battery gauge display with one side 0 and the other 100%

https://www.aliexpress.com/item/1005001421552415.html
https://www.aliexpress.com/item/1005003719349382.html

[DavidAlfa]

The problem with servos and actuators is that the indicador will keep showing "ON" if the power is suddenly removed.

[Terry Bites]

Us Europeans are worried radiation trefoils may become be a common sight!
Actually, I think these flag things were used on trains

[SilverSolder]

That's amazing. I didn't know anything would be visible at that level. My previous thought was that a low batt indicator is a dumb idea. I once had an answering machine that flipped on an LED to warn of low batteries. That quickly drained them, causing them to leak and destroy the device. Brilliant design or stupid design, I'm not sure. As for "any" modern LED, I'd suggest testing it first, and making sure most of the batch was useful at that level if this is a production device.

I prefer the inverse of that:   Indicate that the battery is good! -  if the "good" indication is not there, you know it's "bad"....    and that uses no power!