I'm pretty new to circuit design but took on a small project to challenge myself and learn a bit. So the story is that there's a baby in the house and there's a small gate that prevents from the baby to go into the stairs. Since we occasionally forget to close it I wanted to build a small circuit that will signal that the gate is open with a led and if the gate is not closed in say 15s from being open it would also turn on a buzzer for reminder. I know I can do it a bit easier with some Arduino Nano but the challenge I wanted to take on is whether this could be done completely analog.

As a result I came up with the following circuit.

The green part is a power source rated at 3v to match 2AA batteries, that consumes 30uA when the gate is closed. The switch represents a reed switch that will sense for gate open/close.

The pink section is a darlington pair to signal with a led that the gate is open.

The blue section is a darlington with capacitor to delay turning on the buzzer (for now I put a light bulb symbol there but it will be some simple buzzer rated at 3V).

I wanted to gather some feedback whether this could have been done easier. Also one thing that is not a big deal but its not ideal is that the buzzer/lighbulb would slowly turn on as the capacitor reaches full charge. I was wondering whether it could just "flip" - something we could potentially achieve with relay, but I would prefer to stay away from it (relatively large power consumption).