How can an emergency call works with no network coverage?

In the absence of mobile phone coverage, your mobile phone is telling you "No network, emergency calls".
Isn't that a paradox? How can you make an emergency call with no network coverage?

First, why do we need to cover the network to make calls?

The network towers are an essential component of the phone call process, when you make a call with your friend, the moment you press the contact button, your phone sends a signal to the nearest network tower, and then the signal goes to the nearest tower of your friend. Finally, your friend's phone receives that signal.

Now what's the secret of emergency calls?

You may think it's a mechanical trick or software inside your mobile device, but that's not true.
As we know, phones need a network to make the call, and when the power of the service provider's network (company) is not enough to make the call, your phone will use a network of another service provider.

Most sim cards are powered by GSM Technology, which allows you to use a network of another service provider when your service provider is absent, but your access to the other network is only limited to emergency calls where your phone will automatically pick up a signal from one of the roaming networks. " it is a network of a contracting company with your service company, but if that network is also weak, your phone will contact the best network available near you regardless of its source, and will only be able to make emergency calls.

What if the sim card is idle or non-existent? Can you make an emergency call?

In fact, the sim card is not essential in making an emergency call, it only has the phone number and user information.
The Antenna on your phone will call the service tower even without a sim card, but that service is not available in all countries.
In that case, the emergency center will not be able to identify or locate the caller.

What if there's a complete absence to cover all the servers around you?
Well, if you're somewhere far away from the towers of all service suppliers, that's bad news.