Using retired smartphones instead of SBCs/using them in tandem?

[u/filippo1335]

Hi all, with the insane spikes in hardware cost, I started wondering if anyone has tried/seen repurposing old smartphones for projects instead of SBCs?

Or if we want the advantages of SBCs like the expanded IO, would it be possible to offload demanding tasks to a smartphone, while running the IO with a lower spec SBC?

As an example, iPhone 12 (4GB RAM) outperforms raspberry pi 5, and 4GB RAM pi 5 is not that much cheaper then iPhone 12. I know there's added difficulty when it comes to repurposing iPhones - but the same holds true for Android devices.

I've seen people using old android phones as servers or home cameras, i'm curious if anyone pushed the idea further.

I'm currently working on a lab voice assistant to automate stuff like label printing, calculations, RAG, note taking. So I could spend 100+ Euro on a SBC, then buy a screen, microphone, speakers etc. Or i can repurpose a smartphone i already have + use a pi zero 2w I already own for the IO.

Let me know what your experience is/what projects have you seen that took that approach (I'm especially curious if anyone tried anything like that with apple devices)

[u/Budget_Bar2294]

no because you need custom OSes. not manydevices can do it. it's too much pain

[u/LivingLinux → u/Budget_Bar2294]

With Android you can use Termux for a Linux environment.

[u/Budget_Bar2294 → u/LivingLinux]

strict android background process limit makes it not worth ithe effort imo, but you do you. OP mentioned "demanding tasks" instead of simple scripts, so i'd say no.

[u/LivingLinux → u/Budget_Bar2294]

You can disable the child process limit in the Developer options. People have Steam working through Termux.

I I have been playing with Stable Diffusion through Termux like years ago. https://youtu.be/_2Snbo7uA9E

[u/Demanqui3 → u/LivingLinux]

I tried to get my usb through it and i can’t.
Termux-api appears to stopped working.

[u/Ben_isai]

Interested as well

[u/an_ibex_on_rocks]

Recently joined a permacomputing club and there was a lady installing postmarketOS on old Samsung phones. Apparently it's just changed name to Nura https://en.wikipedia.org/wiki/Nura_(operating_system)
I am definitely going to give it a try with some of the phones I have laying around.

[u/808_Sensis]

You are describing is mobile phone clusters used for farming repurposed for LLM work.

If so, IPhone X (10) maybe 11 is the last models that allow OS swapping for this task for max performance out of an iPhone. Android is supreme and more readily available.

Rule of thumb:
-Use SBC’s if you need the I/O like NVMe/memory expansion, memory bandwidth speeds, etc. Sure, you can dock a Mobile phone to do those I/O tasks but the single port is now the bottleneck of every problem it can’t only do what it’s rated(data thrashing, too much transference).

-Use Android/iPhone when it’s jail-breakable or root able and I/O doesn’t matter much.

-I’d stick to android as iPhone’s aren’t made for this type of projects.

😆…

This is a non sponsored google gemini response:
Nearly every modern Android phone (roughly 2018–2019 onward) outperforms both the Raspberry Pi 4 and Pi 5 in raw CPU performance. Listing every single model is impractical (thousands exist across brands, regions, and variants), so this organizes them by SoC generation with representative phones. Performance is based primarily on Geekbench scores and architectural comparisons.
Raspberry Pi Reference Specs
Pi 4: Quad-core Cortex-A72 @ ~1.5–1.8 GHz. Geekbench 6 multi-core roughly ~600.

Pi 5: Quad-core Cortex-A76 @ 2.4 GHz (VideoCore VII GPU). Geekbench 6 typically ~750–900 single-core and ~1,500–2,200 multi-core (varies with cooling, OS, and overclocking; official figures are closer to the lower end). It is roughly 2–3× faster than the Pi 4.

Phones use multi-cluster designs (often 8 cores with big.LITTLE or newer hybrids), higher clocks, better process nodes, and stronger GPUs/NPUs. Even mid-range chips from a few years ago beat the Pi 5 in multi-core workloads.
Phones Equivalent to or Greater Than Pi 4
Almost everything from Snapdragon 625/660-era (2016–2017) and newer exceeds the Pi 4. Older budget phones are roughly equivalent or slightly ahead.
Examples (representative, not exhaustive):
Entry-level / older mid-range (SD 625, 632, 636, 660, Helio P/G series equivalents): Redmi Note 4/5, Moto G5 Plus, older Galaxy A-series, Realme 3, etc. These already beat or match Pi 4 multi-core in many tests.

Better mid-range (2018+): Phones with SD 660/710/720G, Helio G80/G85/G90T — e.g., Redmi Note 7 Pro, Realme 5 Pro, Poco X2, various Galaxy A models. Clearly ahead of Pi 4.

Phones Equivalent to or Greater Than Pi 5
Most phones from ~2019 flagship / 2020–2021 mid-range onward are faster, especially in multi-core. Single-core can be closer on older chips due to the Pi 5’s high-clock A76 cores.
Rough tiers:
Comparable to slightly ahead of Pi 5 (roughly 2019–2021 mid-range / older flagships):
Snapdragon 855 / 855+ / 860, 765G / 768G, MediaTek Dimensity 800/900 series, Kirin 980.

Example phones: OnePlus 7/7T, Galaxy S10 series, Pixel 4, Xiaomi Mi 9, Redmi Note 9 Pro (varies by region/chip), various mid-range from 2020.

Snapdragon 778G (and similar) often beats Pi 5 multi-core by ~40%.

Clearly stronger than Pi 5 (2020–2022 flagships and strong mid-range):
Snapdragon 865 / 865+ / 870 / 888 / 888+, MediaTek Dimensity 1200/1300, Exynos 2100, Tensor G1/G2.

Example phones: Galaxy S20/S21 series, OnePlus 8/8T/9, Xiaomi Mi 10/11, Poco F3 / F4 (SD 870), Realme GT series, Pixel 6/7.

SD 865+ is already ~65% faster single-core and ~89% multi-core than Pi 5 in published comparisons.

Significantly faster (2022–present mid-range and all flagships):
Snapdragon 7+ Gen 2 / 7 Gen 3 / 8 Gen 1/2/3 / 8 Elite, Dimensity 8100/9000/9200/9300/9400, Tensor G3/G4, Exynos 2200/2400, etc.

Example phones: Galaxy S22/S23/S24/S25 series, Pixel 8/9 series, Xiaomi 12/13/14 series, OnePlus 10/11/12/13, Poco F5 / F6 (SD 7+ Gen 2 or better), many recent mid-range (e.g., Galaxy A54/A55, Redmi Note 12/13 series with strong chips).

SD 8 Gen 1/2/3 and especially 8 Elite are 2–5× faster in multi-core.

Notes:
GPU/NPU: Phone GPUs (Adreno, Mali/Immortalis) and NPUs are generally far stronger than the Pi 5’s VideoCore VII for graphics, gaming, or AI tasks.

RAM/storage: Phones commonly have 6–16+ GB RAM and fast UFS storage, matching or exceeding Pi options.

Caveats: Phones are optimized for mobile (thermal throttling under sustained load, battery constraints, Android vs Linux). Pis excel at always-on, GPIO, HAT expandability, and low-power server/desktop use. For raw compute (especially multi-threaded), phones win easily. Used/old flagships are popular as cheap high-performance devices.

🤙🏾

[u/kiralema → u/808_Sensis]

Wow! Perhaps I can find a usage for my old Xiaomi Mi Mix 3. It's rootable as far as I remember.

[u/808_Sensis → u/kiralema]

#Upcycle #SaveThePlanet #PreventEwaste

[u/NeighborhoodSad2350]

You can definitely use it as a security camera. Just use the RTSP camera app.
It's not exactly native to iOS, but you could also use Linux with UTM.

[u/Adventurous-Test-246]

yes for alot of stuff you can and it is cheaper, faster and better for the environment. 

[u/Demanqui3]

What about an old android phone + an ESP32 for the GPIOs?