The Amazon Echo can be activated by voice "Alexa", even no internet connection. How can i implement such feature on my development product.
Regarding the wake word: How you trigger the recognize is entirely up to you. If you want to use a wake word library to detect Alexa and then trigger a recognize request to the cloud that should work fine. At the time of this writing we don't have sample code available that demonstrates a wake word implementation.
Regarding the alerts: Your client implementation should handle this case. Once you receive the SetAlert directive with the time that the alert should be saved somewhere on your client. When your client starts (even if it doesn't have internet connection) it should check where you save alerts and then schedule a task to alert the user when the alarm goes off.