You would have to know exactly what you're doing before going with a DIY approach of an airgapped device. This includes generating your seedphrase completely offline and never letting your private keys online even when signing transactions.
If you know what you're doing, it's a good approach, but definitely not 'zero' investments. You are dedicating a device entirely for your storage, and hardware wallets are not comparatively more expensive than cheap mobile devices.
It's important to understand the importance of seed and private keys only then you can define a strategy about how to secure them. Mostly we don't take the security of seed and private key seriously unless we meet with some accident. The sooner we realise the importance of security in Bitcoin the better it is.
The thread is no doubt worth reading and most of replies are against the use of mobile phone. There are many thing worth noticing in that thread but the best one I find is from
o_e_l_e_o (Hope he is doing good.)If there is no precautionary measure in your electornic device then don't blame the hacker, blame yourself.
As they said --air-gapped smartphones are much safer than the air-gapped PC which are vulnerable to hacking, did you know that even fully air-gapped PC can exfiltrate information through the output radio signals generated by the computer or call [electromagnetism].
If someone knows enough about your set up to make you a target for such an attack, can gain access to your airgapped computer, bypassing all physical and all electronic protections you have in place in order to install the necessary malware to start transmitting your private keys via modulating electrical signals in various internal components, as well as bugging your house with the necessary hardware in order to pick up and transmit those signals, then every single wallet you own is at risk (not to mention literally everything that you own). Such attacks are almost entirely theoretical.
I keep seeing people telling that phones are hard to airgap and.. sorry, but I'm not convinced.
I will never trust a software airgap (i.e. a phone with airplane mode turned on or WiFi turned off) as much as I will trust a hardware airgap (i.e. a computer with no WiFi card). It is almost trivial to open up a computer and remove the WiFi card, ethernet card, etc., while it is almost impossible to remove the antenna, WiFi, Bluetooth, NFC, RFID, etc. from your average smart phone without breaking it in the process. And how does the average person verify that airplane mode is doing what you want it to be doing. Even the NSA have admitted they can still track phones which are in airplane mode, so your phone
must still be sending and receiving some data.
