Your electrical panel doesn't send a notification when it's out of capacity. It sends these instead.
1. Breakers trip when two big things run together
A/C plus dryer, microwave plus space heater. That's a panel or a circuit at its limit.
2. Lights dim when a motor starts
The A/C compressor, the garage door, a power tool. A brief dim is normal on a marginal service. Regular dimming is a sign.
3. The panel is warm, buzzing, or smells
None of those are normal. Turn off what you can and call the same day.
4. It's a fuse box, or a 60 or 100 amp service
Fine for a 1960 house with a gas range and no A/C. Not fine for how a house is used now.
5. The label says Federal Pacific, Zinsco or Sylvania
These brands have a documented failure history. Replacement is the recommendation regardless of how it's behaving.
6. You're adding an EV charger, heat pump, hot tub, ADU or solar
Each of those is a large new load, and most of them can't be installed on a full 100A panel without load management.
7. There's no room left
Tandem breakers everywhere, double-tapped lugs, or a subpanel bolted next to a full main. The panel ran out of space years ago.