The Mace Personal Alarm Keychain is compact in size but emits a huge 130 dB shriek! Activate the alarm by simply depressing the button on the front of the alarm. To deactivate, depress the button on the back of the alarm. There's even a built-in backup whistle you can blow into at the bottom of the unit! 1 year after purchasing your personal alarm model, it's recommended you test the alarm to make sure it is ready to go whenever and wherever.