You will never not hear a smoke alarm while wearing ear plugs.

They are effective at attenuating noise, ineffective at eliminating it.

Luckily smoke detectors and true (loud) emergencies seem to punch right through without any issues.

I wear ear plugs every night. The disposable foam ones are good enough to prevent me from being woken up by my partner getting ready before me, but I would most certainly hear a fire alarm. I'm laying in bed right now with them in and I can still hear the fan pointed at me. They significantly reduce low-mid range frequencies, but they're not 100% soundproof