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how to make an IP address public so devices can connect and use the computer connected to the IP as a websocket server

The concept is simple:
A smartphone has an app that has only 1 button, pressing the button makes a call to a websocket server (my PC, the websocket runs in background on startup) when the websocket recieves the button's press it shutsdown the pc, i have all the logic and code ready but i need to know how to make it so that whenever the 2 are (es. pc in London, but phone in Italy) they can still communicate with eachother. i thought of using port forwarding but i don't know much about networking and how it works. Is there a way to make the IP public or port forward the router so that it achieves what described above? note that i don't care much about the security of the app because i am the only one who will be using it.
P.S. the code is written in c#.

Check if another device is alive on the network based on its IP-address

I'm trying to write a simple UWP IoT App that is to run on Windows 10 IoT Core on a Raspberry Pi.
The App need to test if another device is currently alive on the local network. All the Apps knows about this other device is its ip address.
I see from other SO questions that Ping is not supporten because ICMP is not supported on WinRT. I assume this also the case on UWP?
I guess I could create a socket and try an connect to for example port 80 and unless a time-out error is received then that means the device is available. However that "hack" seems a bit messy and I'm not sure that it would be solid enough to rely on.
Any other ideas for some C# UWP code that can be used for testing that a device is available and alive on a local network based on its ip address?

You are correct, ICMP is still not supported on UWP. But you could use this instead: https://github.com/christophwille/winrt-vasily (it's kind-of what you wanted to do, but already done)

Android UDP broadcasting works but direct IP not working

I've published an Android app which communicates with a C# server app via UDP. I've implemented an "Auto Connect" feature which does broadcasting and receives an answer from the server. Once an answer received by phone, the phone app holds the sender IP and sends subsequent messages to this IP directly. Also there is a Manual Connect feature which sends data to the IP address the user enters (which is the local IP of the PC running the server app).
So, everything works great for lots of users but some users reported me that when they use manual connect, it never connects; when they use auto connect, the server gets the broadcast message (seems connected) and the phone receives the answer but afterwards none of the (direct) messages will be received by the server app. The common point of these users is that their PCs are connected to the WiFi router by wire and their phones are connected by wireless. I've tried the same thing on my network but again it works for me without any problem.
May it be because of having multiple network interfaces (both LAN and WLAN)? I've been searching net for 1 week but no success.
What should I do? Please help.
Thanks in advance.

Send data from the server to a GPS device

this is my first question here, after searching and reading through many places I have not choice but to ask.
I have a C# application that receives data from a GPS device and stored in a database, I need now is to send a string that contains commands which the device should be interpreted.
This device connects to the Internet over GPRS, I haven't idea how to send this packet over TCP over GPRS because the IP is dynamic.
I hope any suggestions or ideas on how to solve this.
Best regards.

You should do it the other way around - the device should poll the server for instructions. Just make sure the server is accessible.

As you have specified that you have developed a C# application to read the GPS data through GPRS that means you are running C# application on a public/static IP.
Nwo as soon as you get a request from the GPRS client, you get the DHCP IP address of the remote endpoint too.
Once you have that endpoint and socket open, you can transmit any data to the GPS device back.
Assuming that your GPS device is having some microcontroller to drive the GSM/GPRS modem.

I'm going to make an assumption here that the 'Device' is some kind of mobile phone connected to a standard GSM network?
If it is, then the short version of the story is "Forget it" even if the IP wasn't dynamic, you simply wouldn't be talking to the IP of your device, you'd actually be talking to the IP address of your providers GGSN, and for a standard consumer connection this is going to be where the buck stops.
Now that said, IF you have the budget, and all your devices (Assuming multiple ones) are with the same carrier, then you can approach the carrier and request a dedicated APN (Access point name) essentially what this is , is the mobile network equivalent of a DNS record, or at least similar enough to use that analogy anyway.
When you set up your data connection on your device you may recall having to enter something like 'pp.vodafone.com' or 'INGhub411.o2-uk.inbound' we'll this is your actual APN, and if you have a custom one they your devices can be set up so that the IP the presents itself at the GGSN actually has a static route back to the individual device in the suppliers GSM network.
As a general rule of thumb however on consumer grade connections this is not enabled and hence there is no ingress available to the individual device.
As zmbq says, the ONLY option you have is for the device to keep polling the server on a regular basis, and yes unfortunately that is going to be very unforgiving on the battery.
of course there is one other way of approaching this, and that's to have the device open a socket directly to your server then keep that socket open. Once the socket is open, 2 way communication can be performed across the link, unfortunately your going to also have to write all the code to manage this connection including, but not limited to monitoring the connection to make sure it's still open and re-establishing it if it's not, something which is incredibly important on a mobile device.

Getting a notification when my system freezes

I have a minor problem where my (new) computer tends to completely freeze up. Am not sure when it happens exactly but the 6 times that it did happen during the last 4 weeks, it could have been related to a very long rendering task that eats up lots of RAM. (Am actually pretty sure that this rendering engine is causing this problem.) Anyway, I don't really care about what causes the problem. I can repeat it by having the same image rendered again and waiting about 4 hours for it to finish. And I can avoid it by making a minor adjustment to the rendered image which somehow seems to solve it all. It's likely a bug in the rendering engine.
And when I say Freeze, I mean that everything stops responding. Keyboard, mouse, disks, they all just stop and the image on my screens are frozen. I don't get a BSOD or automated reboot.
I don't mind the freeze-up, but I would like to receive a warning when the system does freeze up. So I was thinking about a simple solution that should warn me when it does freeze up again. To do so, I want to use an old SmartPhone (HP IPAQ) which runs Windows Mobile 6 and connect it to my computer through one of the USB ports. It would just continue to communicate with my computer to check if it's still alive. When the computer doesn't respond for 5 minutes, it will assume the system is frozen and would have to send a signal to me. Basically, I want it to send me an SMS message to my other phone. Well, consider the SmartPhone to be a kind of lifeguard...
Anyways, I am quite familiar with software development, just don't know where to start with this application. I will be using the .NET Compact Framework and need some pointers in the right direction to do the following:
1) How to connect to a service on another PC using the USB connection and not some wireless Internet connection? (And definitely NOT any Internet over GSM options, since it's just a prepaid card that I'm using for this phone.)
2) How to send an SMS message from this phone to my other phone?
3) Are there already some existing solutions similar to this thing I just came up with, which could save me some time programming?

I used to have an iPaq pocket pc and based on what i remember when you hook them up to the pc they pick up an IP address.
That IP address is the key to your problem,
your computer could ping your pocket pc's ip as a heartbeat. that way you can be sure that you aren't going through GSM since the Desktop is calling the handheld. How to: Create a Socket Listener your socket listener would be listening on your pocket pc if it doesn't get any messages in a set period of time it would trigger the alert winch would send out your SMS.
You could also do the reverse, where your pocket pc would be pinging your desktop, just make sure that you are using the local IP to avoid traffic over GSM
Sending SMS using compact framework
Send SMS Sample

1) You can connect to a USB port as a COM port - many examples on how to do this especially around using GPS. Write an app for your pc to listen to USB for a message and respond. Write the app on the phone to periodically send a message to the PC and get a response.
2) There should be an API for the phone to send an SMS.
3) Not that I know of, the closest being anything that communicates on USB such as I mentioned with GPS-enabled devices.
Good luck - I know (since I have worked with all the technologies you are talking about) that I wouldn't have a problem making this, but for those without that experience it could get tricky.