在Android系统中用来显示界面的组件（Component）为Activity，也就是说只有重写Activity的onKeyDown方法来监控/拦截/屏蔽系统的返回键（back）、菜单键（Menu）及Home键。

1、拦截/屏蔽返回键、菜单键实现代码

@Override
public boolean onKeyDown(int keyCode, KeyEvent event) {
    if(keyCode == KeyEvent.KEYCODE_BACK) { //监控/拦截/屏蔽返回键
        processExit();
        return true;
    } else if(keyCode == KeyEvent.KEYCODE_MENU) {
        //监控/拦截菜单键
    } else if(keyCode == KeyEvent.KEYCODE_HOME) {
        //由于Home键为系统键，此处不能捕获，需要重写onAttachedToWindow()
    }
    return super.onKeyDown(keyCode, event);
}

2、拦截/屏蔽系统Home键

public void onAttachedToWindow() {  
     this.getWindow().setType(WindowManager.LayoutParams.TYPE_KEYGUARD);     
     super.onAttachedToWindow();    
}

为什么必须重写onAttachedToWindow()，看看下面的代码就知道了

/frameworks/policies/base/phone/com/android/internal/policy/impl/PhoneWindowManager.java 1000行附近
if (code == KeyEvent.KEYCODE_HOME) {  
    // If a system window has focus, then it doesn't make sense  
    // right now to interact with applications.  
    WindowManager.LayoutParams attrs = win != null ? win.getAttrs() : null;  
    if (attrs != null) {  
        final int type = attrs.type;  
        if (type == WindowManager.LayoutParams.TYPE_KEYGUARD  
                || type == WindowManager.LayoutParams.TYPE_KEYGUARD_DIALOG) {  
                // the "app" is keyguard, so give it the key  
                return false;  
        }  
        final int typeCount = WINDOW_TYPES_WHERE_HOME_DOESNT_WORK.length;  
        for (int i=0; i<typeCount; i++) {  
            if (type == WINDOW_TYPES_WHERE_HOME_DOESNT_WORK[i]) {  
                // don't do anything, but also don't pass it to the app  
                return true;  
            }  
        }  
    } 
}