Any devices that will alerts with an audible alarm for AFIB?

None that I know of. While there are many detectors, from finger pads to smart watches and smart rings, none of them is meant to run continuously, especially on a small battery, and none of them have the provision for alerting the person when it happens....not in real time. I am not familiar with the Apple watch function, but the Samsung I wear, and the various Kardia devices, and the various rings, will give you sleep data and HR data, plus an ECG occasionally. Just not an alarm if you go into AF.

Interesting question. Most of my episodes have started at night.

I don't have an Apple watch but do have a Fitbit watch. It monitors for aFib but technically not constantly. It monitors in some format of overlapping time periods. But I often wonder of the accuracy of these personal monitors. Consider the process of having an ECG at your doctor's office where you're usually on a table, not moving and reasonably calm. This is considered the "standard" method. Now we use a watch with one contact surface and no doubt some form of AI to produce a variation of the "standard". Makes me wonder sometimes.

I just saw on affibers.org that someone posted that her Galaxy 7 watch does alert her. It awakened her one night with a haptic sensation and the watch face said she was in AF. So maybe we're making progress...?
https://www.samsung.com/ae/support/apps-services/real-time-atrial-fibrillation-notifications-with-samsung-health-monitor/#:~:text=Samsung%20Health%20Monitor%20is%20a%20feature%20that%20provides,of%20AFib%2C%20so%20they%20can%20seek%20medical%20attention.?msockid=0201a5746a77642733f9b0936b8765b8
(The URL doesn't look like it should work, but I just tested it and it works.)

I am worried that my husband will go into AFIB while sleeping. We are new to AFIB, sadly, and he is completely unaware when it is happening. Yeesh. I don't like the idea of spending my life without him in it.

AF is not a lethal disorder. It can lead to problems if left unmanaged, so it should be managed. But I'm talking about months, years...not a few weeks. You are worrying needlessly. The single most important caution is about the risk of stroke which takes place within a few hours of the onset of AF. Therefore he should be prescribed a regimen of anti-coagulant, whatever works for him....safely. A cardiologist would know to do that immediately. Other than that, the other problems come months down the road, and some of it is reversible if the AF is fixed.....fixed...not cured. There is no cure, but it can be 'fixed', especially via the gold standard treatment known as catheter ablation. It's a day procedure, and it works wonders to stop AF from happening most of the time.

My Fitbit will supposedly alert me also via vibration and a notification on its face. So far never a notification in 5 years. But as they say the devil is in the details. If you dig into the process the watch uses to detect heart rhythm issues it's a pretty complicated process for at least me to wrap my head around. No wear as simple as laying on a table with 12 leads stuck to me.😊

I have a Fitbit. It monitors for AFIB while I sleep. Almost every episode I've ever had has started while I was sleeping. I also have a Kardia 6-lead. Any time that I wake and have a notification that I was in AFIB, I immediately check on the Kardia, and my Fitbit has been correct, every time. Having most of my episodes at night actually seems safer, and causes me less anxiety. Try to relax... AFIB is not a death sentence. Just stay on top of it with his cardiologist and EP. Hang in there!