Late for school

It was the first time ever this year I was late for school. And I had a very good reason which is that last night there was a power trip in my house and the whole house's digital alarm clock was reseted. So the alarm clock did not ring at 6.30am, resulting in me waking up at 7.10am and reaching school 1 minute late. So, Mr Raj (School's operation manager) asked me the reason why was I late. So I told him the TRUTH, and this was his reply : "Telling me such a common excuse and expecting me to believe it?" (He said something like this). His deficient speech made me feel like skinning him alive >:(
And there was something that made me wonder if the school is biased. The school often check on late comers bag for prohibited items (hand phones, cigarettes, drugs, ect). They do not even bother to check the bags of those students that come to school on time. I can tell that more than 85% of the students in the school brings their hand phones to school daily. By only checking on the late comer's bag, are they trying to tell us that if we come to school on time, we can bring prohibited items to school? So in the future, all drug traffickers can get away scott-free as long as they come to school on time? I feel that the school should be fair by having this term "One for all, all for one". If they want to check our school bags, check EVERYONE's school bags, if they are lazy to check, then don't check at all. The school will say that they only check on late comer's bag as it is a "Punishment" for late comers, but I will say that it is "Laziness" of the school. This act by the school shows us how lazy this school is to check all of our bags right?