A good rule of thumb is that if your phone has a headphone jack, it also has FM radio. And whether it has a headphone jack depends on whether the phone aims to be waterproof.

Waterproof phone = no headphone jack = no FM radio. There are some exceptions, but it's more often true than not.

How come different connector can be sealed but jack not?

the USB connector is a box that is not open to the inside of the phone, at least every one i've seen. I've even seen a couple of phones where the box that held the USB connector also had a speaker in it. I guess a headphone jack could be put inside of a similar box, but the main difference is all the contacts in TRR plugs are spring metal that are attached to the outside of the plastic housing and poke through, and that's if the spec calls for any sort of reinforcement. The simplest headphone jacks are just spring metal in empty space.

They can, but it's much much cheaper to get rid of them altogether.

> Waterproof phone = no headphone jack

The Asus Zenfone 9 has a headphone jack and is rate IP68 (up to 1.5m for 30 mins):

* https://www.asus.com/mobile/phones/zenfone/zenfone-9/

* https://www.gsmarena.com/asus_zenfone_9-11656.php

The iPhone 14 Plus is also IP68 (up to 6m for 30 mins):

* https://www.gsmarena.com/apple_iphone_14_plus-11862.php

GSM Arena's search criteria shows >200 phones that have 3.5mm jacks and IPx8 IP Certification:

* https://www.gsmarena.com/search.php3

> GSM Arena's search criteria shows >200 phones that have 3.5mm jacks and IPx8 IP Certification

Released in last five years: 303 with IPx8 certification, out of which 122 also have a headphone jack.

So out of every three waterproof models, two don't have a headphone jack. Seems to support my rule of thumb.

Your rule of thumb is wrong a third of the time which is a D grade.

Technically passing, I suppose.

Yes, that's what rule of thumb means.

It doesn't imply it's always the case, just more often than not. >60% is more often than not.

I think you're a bit off on what rule of thumb means. Something that's false 1 out of 3 times is not "generally true".

If it was a 51/49 split in probability would you still call it a rule of thumb?

Every Samsung galaxy flagship from the S4 to the S10 had a headphone jack and was waterproof. This heuristic only works for recent models where headphone jack means it's a budget model and they've probably skimped on waterproofing.

> A good rule of thumb is that if your phone has a headphone jack, it also has FM radio

Another good rule of thumb, if your device was intended to be sold in the US, then the carrier had the radio disabled for anti-consumer reasons.