I have always liked the thief approach,for instance grappling hook from adjacent building, then rapelling down to the window of an empty office.
How about he sets off the alarm on purpose, then enters the building while it goes off(ofc in another part of the building).
Or he sets off the alarm multiple times, in response they get service crew to take alook. He lies in wait for the maintenance people and uses for instance the neuralring i suggested earlier to knock em out. Uses a special device to put his own pic on id card,then simply walks into the building.
Use a Higher Power. Infiltrate or impersonate some sort of an authority that can force its access to the premises. Not exactly covert, though.
A child porn raid targeting a specific employee's computer, or a blanket "audit" of all the machines in the facility for software licensing compliance, are just two of the many possibilities. The latter may also allow insertion of malware or listening devices in relative comfort. Other possibilities can involve an immigration raid, workplace safety inspection or other kind of compliance enforcement annoyance, or even just calling in a bomb threat and letting the bomb squad do our dirty work.
The bomb threat may also serve a role if we want to "depopulate" a surveillance camera supervision center for a while.
Schneier in "Beyond Fear" describes a bank robbery. A volcano erupted, covering a nearby city with ash. City got evacuated, then completely buried under ash. Shortly afterwards the enterpreneurs came, dug a hole through the ash into the bank, and removed the money.
For gaining access to data or materials in a facility, a catastrophical event can be exploited (e.g. a flood) or staged (a fire). Data recovery from flooded or fire-damaged disk drives is commercially available. Access to a freshly burned-down or flooded facility may be made easier by the damage done to the security system, and the overall chaos of the situation.
The Spy commissions the "ImproVision" Company to organize a "power breakfast" to discuss the optimal application of "country originated social standards" in "factory boats" operating near EU countries.
This attracts syndicalist, journalist, corporate suits, lawyers, politicians, etc....
Of course the Spy is "donating" the catering services, technical setup etc...
This enables him/her to have a dozen of people with :
- badges to come in
- excuses to be clueless if they happen to be in places where they are not supposed to be.
Brings a newbie agent and asks for ideas to distract the guards. intern looks at building rubbing his chin" we could...-insert ridiculous idea here-.. in the meantime the older agent pours zippo gas on the back of newbie jacket.
"sounds like a plan kid..by the way, you are wearing the special suit i gave you?"
"yeah boss!" "great kid! now dont take this the wrong way..(pats kid on shoulder)you are the distraction" "uh...what?" sets him on fire,calmly and unaffected watches the burning newbie sprint past the building screaming hes on fire, with guards running after to help.
" Good work hotshot, you are on fire today"walks into building(if you use neveen´s idea for obsession with smelling stuff he could take a whiff of the the zippo gas first:-)