[mdasen]

As you note, it would be defeatable by putting your phone into airplane mode. However, if you're having a party with 30 people, I doubt you'll be able to get a majority of them to turn off their phones. If the owner gets ping'd if there are more than 10 people, I think it'd be hard to get 20 out of 30 people to turn off their phones before entering the party. Even if they turn it off after arriving, the box might have already registered that the device was there. I think enough people would think "what's the harm" or "I don't want to miss texts from people" that it would be hard to get people to comply with turning off their phones.