PA-28 student pilot reported the alternator failed and they were running low on fuel so they diverted to the nearest suitable airport.

Narrative

This flight is a normal cross country flight from ZZZ1 to ZZZ. There were 3 persons onboard; myself; another private pilot; and a flight instructor. Everything was usual until we were getting into ZZZ airspace; getting ready for an instrument approach. Suddenly; the GPS screen turned dark and we realized that we lost the alternator; then we lost comm 1. As we were trying to switch to comm 2; and notice ATC of the issue. We lost Comm 2 as well; and eventually our transponder. My Flight Instructor then tried to make a phone call; but the phone signal wasn't stable and was not able to notify them of our situation. We make the decision to go back to ZZZ1; so I did the 180 degrees turn. As I was turning; I could hear the ATC says; 'Aircraft X; turn heading 360 if you can hear me'. I tried to talk back to them but nothing works. I then followed heading 360; to buy some times for my Flight Instructor to make phone call to someone. However; when we were over flying ZZZ2; we noticed that our fuel was running low on the left tank.Without a fuel pump; I then switched to the right tank; and verified that the fuel pressure is still in the green. Unexpectedly; the fuel indication from the left tank continue to decrease; even after we switched the tank; and eventually read zero. Without hesitation; we decided to do an emergency descent down to ZZZ2 while maintaining in VMC; and landed safely in ZZZ2. Even though we were on an IFR flight plan; we were in VMC for the entire flight. The main cause of this was the failure of the alternator. Also; I think that the ammeter is one of the things that pilots pay less attention to compared to others. We didn't lost the electricity in a snap but was slowly losing it. If we had spotted the issue earlier; then we might have notify ATC that we are losing power; and prevent a loss communication situation. Having a handheld radio on board could also help.