Status bar > Selection Lock Toggle
Keyboard > SPACEBAR
Selection Lock Toggle toggles selection locking on and off. Lock selections so you donÆt inadvertently select something else in a complex scene.
When your selection is locked, you can drag the mouse anywhere on screen without losing your selection. The cursor displays the current selection icon. When you want to deselect or alter your selection, click Lock Selection again to turn off locked selection mode.
When you want to select something and you canÆt, it's frequently because you have locked your selection.
This button is off by default.
Click to turn it on (it turns yellow). When Lock Selection is on, you can click anywhere in the screen and the program interprets it as clicking the selected object(s). This is useful when you want to keep objects selected while you make a different viewport active or when the selection is tiny, or crowded and difficult to select.
Procedures
To transform an object without touching it:
Use the Select by Name icon in the main toolbar or the H key to select the object by name
Choose the transform icon (move, rotate or scale) from the main toolbar
Press the SPACEBAR to lock the selection set
Press and drag anywhere in the viewport.
The object transforms even though your cursor is not touching it.
To avoid accidentally canceling a selection:
Make your object selection.
Click the Lock button in the status line, or press SPACEBAR to turn on Locked Selection mode.
To exit sub-object selection mode, do one of the following:
In the Modifier Stack display, choose the object level.
Open another command panel. This turns off Sub-Object selection.
If you've turned off Sub-Object selection and object selection is still not restored, one of the following may be true:
Your selection is locked. Turn off the Lock button on the prompt line.
You've set the Selection Filter in the toolbar to a specific category of object, so you can't select any of the other categories. To fix this, select All in the Selection Filter list.