Unfortunately there is no “voice” security built into Alexa the way you are requesting. There are some things you can do, though.
- Disable “Voice Purchasing”. In the Alexa app, under More, then Settings, you can select “Account Settings”, then Voice Purchasing. When this is disabled, you can are unable to purchase items using Alexa with your Voice.
- Set up Guest Connect. In the Alexa app, under More, then Settings, you can select “Account Settings”, then Guest connect. This lets your friends and family connect their Alexa account to your compatible Echo devices for music and news, but only for 24 hours – then they will need to reconnect. You can allow Guest Connect or disable it.
Hope that helps!