I also have a "haptic test" function: press the button, the phone vibrates briefly. I originally created that check the delay on the Pebble-Tasker connection, but ended up using it almost every day to find my phone among the clutter in the house.
Tasker is amazing, if you have Android, I recommend checking it out.
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[0] - misplacing a phone while having it still in Bluetooth range actually happened to me once long ago with a feature-phone. I looked and looked and couldn't find it. It was set on silent, so calling it didn't help. Then I noticed it's still connected via Bluetooth to my PC's phone management app, so I manually turned the ringer on, and discovered it deep within the mechanism of my bed. Finding it there without this trick would probably take me hours.
Better off forcing a ring in the home than where you can't foresee the consequences.
In the same sentence as performance and a restaurant, not less.
In contrast (and yes, my intention was contrast), if the wife was hiding from a shooter then her ability to maintain silence is required for life. Airplane mode isn't great, because she should be texting/tweeting/etc.
Thus, best to not let your silence be overridden.
For non-life-safety reasons that the husband might be trying to reach the wife, that could be solved via agreement ("keep your ringer on except in emergencies") instead of brute force.
For instance, my wife has her phone ALWAYS set to silent. I like all the suggestions here.
I think the "active shooter" situation is a bit of a stretch, to be honest.
"the kid is vomiting and school needs us to come get them asap, which one of us is more available?" is not a life-threatening emergency, but it's a family emergency and needs attention. It also happens a lot. An awful lot more than your "unlikely to happen to most people in their lifetime" contrived scenario.