Bio-mechanical aura - Transformers Wiki
A bio-mechanical aura is a field around a Transformer that is generated by their primary system programs (i.e. their personality programs). It can be used to identify a Transformer and determine whether they're dead or not.
Fiction
Marvel The Transformers comics
Hi-Q Prime knew Dynamo had led him and the rest of the Neo-Knights to the location of the Last Autobot because he could feel the remains of Primus's aura there. The Last Autobot?
Bludgeon refused to believe Optimus Prime had returned because he had felt Prime's aura leave him. End of the Road!
Universe comic
Trailbreaker noticed that the cages he and the others had been put in reacted to each individual attempt to break free and suspected that they were keyed to their specific bio-mechanical auras. He urged Silverbolt, who was put in the cage next to him, to perform a primary system program transfer with him so that they could break free. After escaping and causing a mass jailbreak, they went through the process again to return to their own bodies. Escape