One of the most convenient features of the newer iPhones is to have Siri always listening whether you have power connected or not. Any iPhone with the M9 chip can listen for the key words “Hey Siri” all the time and act upon any requests you give. Periodically something that sounds like “Hey Siri” can activate Siri. Normally instances such as this are few and not a real issue.
My brother and I live only minutes from each other, and we each have an iPhone 7 Plus. While he was visiting I asked Siri for some information by first saying “Hey Siri.” His iPhone responded. After further testing we found that both iPhones would respond to my voice as well as his when we said “Hey Siri.” I never thought we sounded that much alike, but apparently Siri does.
You can disable Siri entirely by going to Settings > Siri > Siri. This will completely disable Siri but when you enable Siri again, you have to retrain your voice. A much quicker way that avoids this is to quickly turn the iPhone on its face. When the iPhone is face down, the proximity sensor stops Siri from listening. As long as the top front of the phone is blocked, Siri cannot listen. That’s why it’s very difficult to get Siri to respond while in a pocket or bag.
With the holiday season here, you may have family visiting with voices very similar to yours. If Siri is activating at inopportune times or answering requests from the wrong person, simply turn your iPhone face down or drop it into a pocket. It’s a low tech solution to a high tech problem.