def set_monitor_det(det):
    """
    Designate one `AmiDet` as the monitor.

    The monitor det is the default normalization detector and the default
    filtering detector when no detector is provided.

    Parameters
    ----------
    det: `AmiDet` or ``bool``
        The detector to set as the monitor. Alternatively, pass in ``False`` to
        disable the monitor det.
    """
    if det:
        globals()['monitor_det'] = det
    else:
        globals()['monitor_det'] = None
