An owner lockable contract.

OnOff.sol

pragma solidity ^0.4.21;

contract OnOff{
    
    bool public kill_switch = false;
    address Owner = msg.sender;
    
    modifier IsOwner(){
        require(msg.sender == Owner);
        _;
    }
    
    modifier checkLock(){
        require(kill_switch == false);
        _;
    }
    
    function toggle(bool On_Off) external IsOwner{
        kill_switch = On_Off;
    }
    
    function message() public view checkLock returns(string){
        return("Hello, we are open for business!");
    }
}