A padlock from a Bangkok hostel is probably the worst lock you could own. Those things cost less than a street pad thai and half of them pop open with a bobby pin in two seconds. Real thieves target hostels specifically because they know everyone's using cheap locks from the guy down the street. A $12 lock at Khao San Road is just a sign to anyone watching that your bag is worth grabbing. Buy a decent lock once and stop carrying around a souvenir that gives you a false sense of safety.