Dear friend,
There are few things that need clarification. Yours if corporate office hence there is no security guard as such. Nevertheless, for an office where 30 employees work, whether it is corporate office or otherwise, you need to have security office.
Secondly, few employees leave office premises during working hours. This fact is observed by HR Executive, by then why this fact is not observed by seniors? Does MD also has his office in the same premises?
Thirdly, employees who work in corporate office are laden with lot of work. Most of them are decision makers. They could be working long also. Therefore, you need to check their attendance records. At what time do they come and at what time do they leave. Possibly their justification could be that they are working too long hence some break is inevitable.
Fourthly, do you have specified lunch and tea time break? In corporate office this is little hard to implement, nevertheless, we need to have information on this count also.
Lastly, as Mr Nathrao has pointed out, did you discuss this matter with your senior? You report to whom? If you report to GM(HR) or even HR Manager then what are his/her views?
There are so many issues associated with your post.
Thanks,
Dinesh Divekar