Вот такой код
MyWidget::MyWidget(QWidget* parent)
{
...
    m_button[2]->setGeometry(QRect(QPoint(50, 450), QSize(100, 50)));
    m_button[2]->installEventFilter(this);
...
}
bool MyWidget::eventFilter(QObject* watched, QEvent* event)
{
	if (watched == m_button[2])
	{
                if (event->type() == QEvent::MouseButtonPress)
		{
			/*Mouse down button event */
			qDebug() << tr("Monitor button event, button press event");
			return true;
		}
	}
}
	m_button[2]->installEventFilter(this);

