One segment of the access control market that never seems to take off are 'Digital Locks':
These products typically feature retrofit mechanical locks opened by exotic keys that log when/where it was used. Even though a 'digital lock' key may fit a lock, unless specific privileges are granted that allow the keyholder access, it does not unlock the door. Also, the key's data is periodically downloaded for auditing and refreshing privileges.
In this way, provisional access control is maintained, without the expense of outfitting every door with new access equipment. (See our: Digital Locks / eCylinder Tutorial for more detail.)
However, compared to traditional electronic access, there are some big weaknesses. Keys usually are expensive ($80 each is not uncommon) and instant 'Lockdown' manageability of doors is not possible, among others.
Despite not seeing 'Digital Locks' be a big factor, there always seems to be new products and new entrants in that area. I am always a little surprised by this.
Does anyone have success selling or using these products?