While the ALT key only works with a keypad and most laptops don't have a separate keypad, many laptops do have an embedded keypad that is accessible via the Fn key. These keyboard generally have the numeric pad symbols printed on the keys in a subdued manner. On my Toshiba is it the box of keys with the '7', '0', 'M' and '/' at the corners. So to get Ω I hold down the ALT and Fn keys while pressing 'k', 'l', 'u' in sequence.