When you hand a phone over for repair, one of the first things a technician does is look into the SIM slot with a light. They are checking a liquid contact indicator, usually shortened to LCI. It is a small sticker that tells them, with no power and no software, whether liquid has been inside the phone.
What it is
An LCI is a tiny patch of absorbent material treated with a water-soluble dye. Dry, it is white or silver. When it touches water or any liquid containing water, the dye spreads and the patch turns red or pink. The change is permanent. Drying the phone does not turn it back.
Where to find it
- iPhone: on models with a SIM tray, the indicator is inside the SIM tray slot. Remove the tray, shine a torch into the slot and look for a small white or silver dot. Red means it has been activated. iPhones without a SIM tray have indicators inside the body that only a technician can see.
- Samsung and most Android phones: usually inside the SIM tray slot as well. On older phones with removable backs, look in the battery compartment and on the battery itself. Samsung's indicators are typically white with a faint pink or purple pattern when dry, and solid pink or red when triggered.
- Laptops, watches and earbuds have them too, generally inside the casing.
Most devices have more than one, placed near the points where water is most likely to get in.
What does and does not trigger it
Indicators are designed to react to liquid, not to damp air. Apple states that its indicators are not triggered by humidity and temperature changes within the product's normal operating range. A humid day or a steamy kitchen should not turn one red.
They can be triggered by:
- Water entering through the SIM slot, ports or a damaged seal.
- Sweat running into an opening during exercise.
- Heavy condensation forming inside the phone, for example after repeated use in a hot shower.
- Removing the SIM tray with wet hands.
What it means for your warranty
A red indicator is treated as evidence of liquid contact. Apple, Samsung and most other makers exclude liquid damage from the standard warranty, including on phones rated IP68. If the indicator has changed colour, a fault that would otherwise be repaired free may be quoted as a paid repair.
It is not always the end of the discussion. If the fault is clearly unrelated to liquid, some service centres will still honour the warranty, and consumer law in some countries limits how far a maker can rely on the indicator alone. It is worth asking politely.
Why you should check it yourself
- Before buying a used phone. A red indicator means the phone has been wet, whatever the seller says. Corrosion can take months to show.
- After a scare. If your phone took a dunk and the indicator in the SIM slot is still white, water probably did not get past the seals. That is good news, though it only tells you about that one spot.
- Before a warranty claim. Knowing what the technician will see helps you prepare.
Can it be reset or replaced?
No. The colour change cannot be reversed, and bleaching or swapping the sticker is tampering. Service centres check several indicators and look for corrosion on the board, so a single fresh sticker proves nothing and can void whatever cover remains.
If your phone has been wet, the indicator matters less than what you do next. Dry it properly and clear the speaker with the water eject sound. The details are in how to fix a water damaged phone.