How can we get the previous state of the checkbox?

I have a checkbox in my Application like below

 <input type="checkbox" ng-model="vm.somevalue" indeterminate " />

indeterminate is a directive which will change the state of the checkbox when the value of vm.somevalue is undefined. Now when i am clicking on the checkbox from intermediate state, i need to unselect the the checkbox(vm.somevalue=false).

Any helps appreciated!