# How I investigated why my iPhone was running hot > I used USB diagnostics, crash reports, and Xcode Instruments to investigate a hot iPhone, but the evidence did not reveal one clear cause. Author: Flavio Copes | Published: 2026-07-11 | Canonical: https://flaviocopes.com/debug-iphone-running-hot/ My iPhone started running hot, even after I closed every app. Closing apps did not help. That alone told me very little, because iOS system services continue working in the background. I connected the iPhone to my Mac with USB and investigated. Here is what I found. ## A quick warning The tools in this post can do much more than read diagnostics. Some commands can restart the phone, change settings, or interact with running processes. I only used read-only commands. Do not copy commands you do not understand. Back up your iPhone first. ## Check that the Mac can see the iPhone First, connect the iPhone with USB. Unlock it and tap **Trust This Computer** if asked. You can check the USB connection with: ```bash system_profiler SPUSBDataType ``` Look for an `iPhone` entry in the output. This only confirms the physical connection. It does not mean the diagnostic channel is ready. ## Install pymobiledevice3 I used [pymobiledevice3](https://github.com/doronz88/pymobiledevice3), an open source tool for communicating with iOS devices. My advice is to install it in a virtual environment. This keeps it isolated from the rest of the system. ```bash python3 -m venv iphone-tools iphone-tools/bin/pip install pymobiledevice3 ``` Now list the connected devices: ```bash iphone-tools/bin/pymobiledevice3 usbmux list ``` The command should print the iPhone model and iOS version. Be careful with this output. It can include device identifiers. Do not paste the full result in public. ## Read the battery diagnostics The simplest way to get a battery snapshot is: ```bash iphone-tools/bin/pymobiledevice3 diagnostics battery single ``` The output is large. These were the values I cared about: - battery temperature - charging current and voltage - current capacity - cycle count - design capacity - full charge capacity - thermal limiting time - charger errors My battery was around **46.6°C** while connected. It was charging at roughly **11W**, which could contribute to the heat. The battery had 426 cycles and about 94% of its original capacity. I found no battery safety fault or charging fault. This was useful. The battery looked healthy, but something was keeping the phone busy. ## Look at historical resource reports iOS creates diagnostic reports when a process uses too much CPU, memory, or disk. You can list them with: ```bash iphone-tools/bin/pymobiledevice3 crash ls \ --remote-file / \ --depth 3 ``` Despite the `crash` name, this also lists resource-limit reports. I found several reports named like this: ```txt photoanalysisd.cpu_resource-2026-07-11-091228.ips ``` `photoanalysisd` is an Apple system service. It analyzes the Photos library for people, objects, scenes, and relationships. Closing the Photos app does not stop it. I copied only the matching reports to the Mac: ```bash iphone-tools/bin/pymobiledevice3 crash pull reports \ --match '^photoanalysisd.*cpu_resource.*\.ips$' ``` Do not pass the `--erase` option. That would remove reports from the phone. The newest report showed the important line: ```txt CPU: 90 seconds cpu time over 134 seconds (67% cpu average) ``` Now I had a strong lead. Photos analysis had repeatedly exceeded the iOS CPU limit during the previous month. ## Test Low Power Mode iOS does not provide a switch for `photoanalysisd`. Low Power Mode can defer background work, so I enabled it as a test. I waited, then recorded the phone again. This time `photoanalysisd` averaged around **0.01% CPU**. The service was practically idle. This did not prove that Low Power Mode always stops Photos analysis. It showed that Photos analysis stopped during my test. ## Enable Developer Mode Historical reports are useful, but I also wanted live process data. For that, the iPhone needs Developer Mode. The option might not appear immediately. First, pair the iPhone with Xcode: 1. Open Xcode. 2. Choose **Xcode → Open Developer Tool → Device Hub**. 3. Select the connected iPhone. 4. Follow the pairing instructions. Then open **Settings → Privacy & Security → Developer Mode** on the iPhone. Enabling it restarts the phone. After the restart, unlock it and confirm Developer Mode again. Developer Mode exposes additional debugging services. Turn it off when you finish if you do not normally develop iOS apps. ## Record all processes with Instruments Xcode includes Instruments, which can record CPU and memory activity from the iPhone. Open it from **Xcode → Open Developer Tool → Instruments**. Choose the **Activity Monitor** template and select the iPhone as the target. I first recorded for two minutes using **Immediate** mode. Instruments warned that the data volume was too high and dropped some data. I saved the trace anyway, then repeated the test using **Deferred** mode. Deferred mode produced a cleaner recording. ## Export an Instruments trace You can inspect a saved `.trace` bundle inside Instruments. You can also export its tables with `xctrace`. First, list the available tables: ```bash xcrun xctrace export \ --input 'run 2.trace' \ --toc \ --output trace-toc.xml ``` The Activity Monitor trace contained a table named `activity-monitor-process-live`. I exported the second run with: ```bash xcrun xctrace export \ --input 'run 2.trace' \ --xpath '/trace-toc/run[@number="2"]/data/table[@schema="activity-monitor-process-live"]' \ --output processes.xml ``` The result is XML containing samples for every process. Notice that Instruments adds its own overhead. Processes such as `DTServiceHub`, `ptpd`, and `sysmond` become busier while recording. Do not mistake that activity for normal idle usage. ## What the live trace showed The deferred recording confirmed that Photos analysis was idle: - `photoanalysisd`: 0.01% average CPU - `mediaanalysisd`: 0.005% - `cloudphotod`: 0.009% - `assetsd`: 0.32% But other processes were busy: - `fseventsd`: 72.7% average CPU - `fileproviderd`: 42.5% - Twitter: 39.5% - `linkd`: 25.2% - Siri embedded speech: 18.8% - `searchd`: 13.9% - `routined`: 8.6% - `cloudd`: 6.2% `fseventsd` tracks filesystem changes. `fileproviderd` handles iCloud Drive and other providers connected to the Files app. This showed that file and cloud synchronization were active during the recording. Twitter was also surprisingly busy. It peaked above 300% CPU, which means it used more than three CPU cores at that moment. ## Did I find the cause? No. I found several processes doing a lot of work. I also found historical reports showing that Photos analysis had previously exceeded its CPU limit. But none of this proved what made the iPhone hot. The live recording happened after I enabled Low Power Mode. The phone was connected to USB, charging, running Developer Mode, and being monitored by Instruments. Every one of those details changed the conditions of the test. The trace showed what the phone did during those few minutes. It could not tell me whether the same work caused the heat I noticed earlier. ## What I learned Closing apps is not a reliable way to diagnose a hot iPhone. System services continue working after every visible app disappears. In my case, the investigation showed two different periods of activity: 1. Photos analysis had previously exceeded its CPU limit. 2. Low Power Mode deferred that work, but file and cloud synchronization remained busy. The battery itself looked healthy. That narrowed the possibilities, but it did not give me a definitive answer. My advice is to start with the safe checks: - restart the iPhone - enable Low Power Mode temporarily - check **Settings → Battery** - leave the phone locked on Wi-Fi and power overnight - remove the case while the phone cools If the heat continues, use Instruments to record a short deferred Activity Monitor trace. That gives you evidence about what happened during the recording. It might reveal the cause, or it might only rule out a few possibilities.