What is the actual process of transferring power?

I know there is some pomp event, but what are the actual logistics. How is military control transferred? If as they claim could happen and about which they are scared, Trump could do something like martial law, but then he would have to prove some last minute intel from the military.

It would be better if he didn't know, but as part of the logistics of Jan 20, upon leaving the office, he formally transfers power to the military, who then guard it until Biden is sworn in. During that time, they don't transfer the military powers to him because of the intel that is surreptitiously received before the formal transfer of military power to Biden is finished.