On each Alexa device there's a button made available with which you can stop Alexa from listening to you. This sort of defeats the purpose of the device, but at times might be appropriate for the situation. But, ironically, Amazon has not provided a skill to shutdown listening with voice. However, for about $100 and some DIY skills, you can install your own capability to shutdown Alexa's listening capability using your voice.
The solution utilizes a Particle Photon mini-board, a USB port, and an IFTTT applet....More