4. Technical requirements

1. Computer/laptop (the user’s computer where the widget is clicked and the sound is played):
   • Internet browser
     • Chrome, Firefox, Opera, Edge, Safari
   • Speakers
     • any standard computer/laptop speakers that cover the 20 Hz – 20 kHz band (the ultrasonic signal is at 17 kHz)
       
2. Mobile phone
   • Android version  4.3 (API level 18) or newer
   • iOS 8.0 or newer