Luckily, a colleague found my card and handed it back to our secretary. Seems that I forgot it in a meeting room. Thanks everybody for the suggestions anyway.
I started to work in a new company just on Monday. This is a large company and my work place is located in a building complex where all employees are required to carry/wear a company ID to enter the building (this is just a pocket size card with a picture and a magnetic band). I received my ID card on the first day of work and I used it yesterday and the day before to enter the office. But today, I could not find my ID any more. I told the security that I forgot it at home so I was let in anyway, but I'm afraid I lost it yesterday on my way back home, maybe because I didn'the fix it well to my clothes. To be honest I'm not completely sure that I lost it. Might as well find it again later at home but I don't have a good feeling about this. What is the best thing to do in my situation? Should I wait or report the loss to my supervisor immediately? I'm new to this company and I don't want to appear like an unreliable person.