What should I do?
You have several options. You could well take the interview elsewhere, some place where you can take the interview without issues.
Now, if this is not possible, I suggest you tell them about this ASAP. A simple email explaining the situation should suffice.
They can then decide if a better hour can be scheduled or if the alarm is no issue, and you could wait for it to stop ringing (remember to mention that it will last at most 3 minutes as you said).
Edit: Some places you could try having you interview may be:
- You local coffee store, one that has wifi and is not so noisy.
- Some nearby library, preferably one that has rooms or cubicles where you can talk.
- Some nearby park, even better if it has wifi (or you can use your cellphone as hotspot if needed).
- If you could find some Coworking spaces near your home that could be a great option. Probably you may have to pay a fee for its use, but you are guaranteed that you have the resources you need.
- You could also try some public University campus, as those places are often open and not so noisy.
Just remember to test the connection there at least once before the interview (as mentioned by Dan in comments), so you are sure it will cause no connectivity issue during the real thing.