By default, when you say "Alexa" near the Echo Show, it displays a blue line on a screen. If you'd prefer something a bit more obvious, you can make your Echo Show play a sound every time you invoke it.

Alexa can make a little dinging noise when you start talking to Alexa and once you've finished your request. This is handy if you want to make a request of Alexa without looking at your device, like when you're cooking and need to focus on what you're doing. Both sound effects are found in the settings menu on the Echo Show. To find it, swipe down from the top of the screen and tap Settings.

Scroll down in the Settings menu and tap Sounds.

Scroll to the bottom of the settings list and tap either "Start of Request," "End of Request," or both. Whichever you prefer.

From now on, whenever you say "Alexa" you should hear a prompt when Alexa starts listening.