These are car key shells (also called remote keyless entry remotes or keyless entry transmitters).
They are the handheld remote controls that allow you to lock/unlock doors, open the trunk (or liftgate), and activate the vehicle’s panic/alarm system from a short distance. The image shows four common black plastic styles typically used on Benz vehicles (roughly mid-2000s to mid-2010s models)
Button functions
Leftmost fob: Lock, Unlock, Trunk/liftgate release, and a prominent red PANIC button.
The panic button triggers the car’s horn and lights to attract attention in an emergency (or to help locate the vehicle in a parking lot).
Second fob: Basic Lock + Unlock only.
Third fob: Appears to have a single large central button (or a different/blank layout).
Rightmost fob: Lock, Unlock, and Trunk/liftgate.