How to check for water damage before purchasing a used iPhone 4

"Checking for water damage is pretty simple and something everyone should do before forking over your hard earned cash for a second-hand iPhone 4."

If you're trying to save some money and are in the market to purchase a used iPhone 4 from either Craigslist, eBay, or some other local or online seller, one of the first things you'll want to do is check for any signs of water damage. I see several people in my office each week that purchased used iPhones that mysteriously quit working after a few days. As much as we'd like to believe there aren't people out there who would sell us broken or water damaged devices, it happens every day.

While online-only iPhone purchases are convenient, I highly recommend meeting up with someone locally, for example, someone off of Craiglist, before turning to eBay or any other online broker. This allows you inspect the iPhone device before you actually commit to purchasing it, and gives you a chance test it out and check for water damage yourself.

If you can't meet someone locally and need to buy online, request that the seller inspect for water damage and send you images that allow you to see that the water sensors are still intact and that the internals have not suffered any damage or corrosion.

Apple has placed 4 sensors inside the iPhone 4 that make it pretty easy to tell if any part of the device has come in contact with liquid. These sensors are placed exactly the same in the GSM iPhone 4 and CDMA iPhone 4. You want to make sure the sensors are white as opposed to red. If you see a sensor that has turned red, that's a sign it's come into contact with liquid or heavy humidity.

How to check external iPhone water sensors

The easiest thing to check are the two sensors you can see without removing the back of the iPhone 4. I recommend bringing a small pocket or keychain flashlight with you in order to get a good look at the sensors.

Headphone jack sensor

Check the water sensor inside the headphone jack of the iPhone 4

Your first sensor is located inside the headphone jack at the bottom. It's the easiest sensor to find and inspect. Shine a flashlight into it and make sure you don't see anything but white. (Red is bad.)

As a side note, this sensor can come out or become dislodged occasionally. If you don't see one, just move on and check the next sensor. I wouldn't take it as a sign that the seller is trying to be dishonest (yet).

Dock connector sensor

Check the water sensor by the dock connector in an iPhone 4

The next sensor is a square sensor in the dock connector. To see it, hold the phone screen down in your hand and look inside the dock connector towards the middle. On the upper side you will see a tiny white square (or red square if the device has come into contact with liquid). Make sure this one is white.

If both sensors are white, it may not be necessary to proceed any further. The device most likely has never been subjected to water damage. If the headphone jack sensor was missing or you couldn't find one of the sensors, you may want to continue to the next section.

How to checking internal iPhone water sensors

It may seem silly to bring a screwdriver with you to check out an iPhone but it'll seem a lot less silly when it saves the lost money and headache you'd get for buying a water damaged iPhone 4.

There are two sensors on the inside of the iPhone 4 that are easily visible once the back is removed. You can pick up a security screw driver online and a #00 Phillips screwdriver from your local hardware store for a few bucks. You'll need one of the two in order to remove the back.

If you're buying a CDMA iPhone 4 off of someone, you'll most certainly need the security screwdriver. Older GSM models still have standard #00 screws while newer ones have security screws. Remove the 2 screws holding the back plate on and gently push the back up and pull it off. This will give you a clear view of the last 2 sensors and a lot of the internals of the device.

While you're checking the last 2 sensors it's always a good idea to look closely at the internals and make sure everything looks ok. You'll want to avoid any devices that show signs of the following:

  • Obvious corrosion
  • Torn cables
  • Missing screws
  • The battery tab is torn off
  • A large amount of debris or dust inside the device

If all those seem good, you'll just need to make sure the water sensors check out okay.

Battery sensor

Check internal sensors for water damage on an iPhone 4

The first sensor is placed directly over the clip that holds the battery down. Again, just make sure it's white and move on the to next and final sensor. If it isn't white but all the rest are, I'd probably still advise against buying the device as the battery or other internal parts could have come into contact with liquid at some point.

Logic board sensor

Check internal sensors for water damage before purchasing a used iPhone 4

The final sensor is located on a screw holding the logic board in place. If this sensor is white, you're in the clear. If it's not, you'll definitely want to stay away from purchasing the device. This sensor is the closest one to the logic board. If it's red, odds are the logic board has liquid damage and will eventually go out.

Wrap up

Checking for water damage is pretty simple and something everyone should do before forking over your hard earned cash for a second-hand iPhone 4. I would personally consider buying an iPhone 4 if only the headphone jack or dock connector sensor was triggered. If the rest of the device is in perfect condition and the inside has no sensors triggered, I'd say you're okay. A lot of things including living in a humid climate can cause external sensors to be triggered. Apple will actually honor a warranty swap if only one external sensor is triggered due to these factors.

Just make sure if one external sensor is triggered or missing that you check the inside ones. As long as those are okay, the decision really lies with how comfortable you feel and how honest you think the seller is. If they seem irritated or worried about you checking out the device, find another one.

Interested in other DIY, repair, and modding info? Check out the resources below or if you ever decide certain repairs are beyond your skill level, contact PXLFIX regarding mail-in repairs and pricing.

Additional resources

iMore senior editor from 2011 to 2015.

  • Might be a good idea to bring a can of that canned air stuff too. I've only had my 4S for 3 weeks now and the sensor in the charge port is already covered in dust.
  • If im selling my phone I am not letting anyone take it apart before coughing over some money.
  • Word... I was thinking the same thing
  • Amen, same here.
  • Anonymous - You look amazing Amanda! I can\'t bveiele how good it turned out considering you took it yourself. Can I suggest part-time photography and part-time modeling?! : )Take Care,Colette
  • Are there similar sensors on the iPad? Might be looking at getting an iPad 2 once the 3's come out.
  • That last paragraph, with link, sure looks like a blatant paid plug to me...
  • Of course it is. If I run a business specializing in iOS device repair why would I not state credibility and plug my business?
  • The only thing that's helpful here is the how to without removing the back cover. You're a fool if you think most will let you do that. The two you've had are not bright in the least bit. Letting a complete stranger open my phone??
    This is defiantly more of a plug for you , kinda like the article about "best" note app. IMore completely left out UPad, which trumps all those other ones iMore mentioned. I guess UPad didn't feel the need to "donate" to iMore. Yes, I've bought and tried those. No comparison.
  • No one is paying us or "donating" anything.
    And also, please don't be disrespectful.
  • Should be simple for Apple to have an error code pop up if water damage has occurred. I also would not want a phone taken apart.
  • I'm not a jailbreak genius by any standards. Could someone who has jailbroken their iPhone possibly be able to reset/defeat a logic switch that would indicate water damage?
  • basically you need a torx x4 i think screw driver,simply remove the back and then get some kitchen roll,wetten it and place it on the sensor.
  • Four tiny chemically sensitive dots must be cheaper, yet more tamper proof and informative than an electronic sensor.
  • . Even the internal sensors are easy to access. 2 screws and the back pops off. No internals are even touched. I've purchased several used phones and not one seller of an iPhone 4 has had an issue with me removing the back to check sensors. Nor should they.
  • Orher than if Apple notices that the phone has been opened, your warranty is sh!t.
  • There is absolutely no way for apple to know the back was removed. Nothing else is even touched.
  • Great video Ally....but man I hope in the next iOS they fix the focus on the camera cuz it's been killing me ever since iOS 5 came out. :(
  • With the rising popularity of LifeProof cases and also the rising amounts of people installing them incorrectly and/or receiving faulty cases, this is good info. Going to be more water damaged iPhone 4s and 4Ss on the market.
  • Thanks for that Allyson. A very helpful and clear explanation of the checks. Do any other phone makers use similar water sensor dots?
    A friend who designed phones told me that moisture from handling and breath tends to get inside phones and will cause deterioration over time. Do you see such problems, or have solutions been implemented?
  • This was excellent info! The tab in the 30 pin connector on my phone is partially red...all the other sensors are white. Do you know if the moisture from a person's breath can cause the sensor in the 30 pin connector to become red?
  • That's normally the first sensor to get triggered, or the headphone jack. Moisture and humidity can cause that. A person's breath, probably not. But moisture from being in a bathroom while the shower is on or something of the like can cause it.
  • My (non iPhone) phone has a habit of unlocking istelf in my pocket and sending cryptic messages to my friends. The predictive text keeps choosing a word, so my friends often receive very deep, meaningful messages like Be', Was' and Sheep'. Yes, I sent sheep' to my friend Adam. I think he's hating being at the top of my phone book.
  • This Is good info for the external inspection. No way anyone would let you open their iPhone without forking over cash first. First points worthless unless you own the phone.
  • apple cant tell if you take the 2 screws out the bottom. you people are dumb. it is nothing wrong with taking back cover off.
  • Haha maybe because you rank #5 in logoge for Geo Tracker ? Too bad that chick was too dumb to realize that your Geo Visitors tools has nothing to do with her crappy car.
  • I'm not quite sure why people would have trouble with anyone removing the back plate. It's 2 screws and doesn't mess with any of the internals. I've done this several times on several occasions. If I'm buying online I ask the seller to remove the back and take images. The worst response I've gotten was "Oh, ok. I don't know how but if you tell me I don't have an issue doing that." I tell them and they send pics.
    When I've met up with several people I say "Has the phone come into contact with water? They say no." I say "Do you mind if I just pop off the back and just look at the 2 internal water sensors." One guy was somewhat hesitant. I explained it was 2 screws and the back pops right off and he said "oh ok, that's fine" - and I was on my way.
    It's really no different than removing a back on any other phone to check a water sensor underneath a battery. People would probably have a completely different outlook if there were not 2 screws to remove. Which doesn't really make a lot of sense to me considering no one would have an issue if it were any other phone.
  • how can i chek a iphone 4 is case sensitive or block by Company?i bought a iphone second hand but it does not work it say sometime no service some time ok but when i want to call someone it say call faild but interent work properly and i can use i feel so worry about it if it is case sensitive what can i do?i cant contact with seller?
  • I dropped my iPhone 4s in a sink full of water and it sunk to the bottom, it only triggered the one in the charging slot, there for even if one is only triggered it doesn't mean it hasn't hit water, m phone still works without a problem in every way, but one trigger is enough to say don't buy it why check all of them.
  • mhmmm i think you can use "device explorer pro" ore some other app like to test if the sensors are still good.
    It's sure cheaper :P
  • Cool tip - thanks so much - !