Bluetooth compatibility/functionality is not universal as there are many combinations of hardware, software, Bluetooth drivers/profiles, etc and all need to match up correctly to have full functionality. As long as the device that the Sennheiser Bluetooth headset is being connected to supports the appropriate Bluetooth version (usually 2.1 and EDR for Sennheiser products) or higher and the appropriate Bluetooth profiles (A2DP, HSP, HFP, AVRCP) are present there should be no connectivity issues.
NOTE: Often with a computer a device called a Bluetooth Dongle (like the Sennheiser BTD 800) is required to bypass the computer's built in Bluetooth chip and provide the appropriate Bluetooth Profiles and functionality for the Bluetooth headset.
Compatibility issues usually occur when the Bluetooth headset is being connected to a more complex device (like a computer). Many computers' built in Bluetooth chips are designed to support peripheral data input devices (like wireless keyboards) but not audio devices and hence the computers' built in Bluetooth chip does not support the appropriate Bluetooth audio profiles and this creates the connectivity issue with the headset. The computer can recognize the headset as a Bluetooth device but does not have the appropriate Bluetooth profile to interact with the headset. The A2DP Bluetooth profile is commonly used in Bluetooth headsets but often not added to a computers' Bluetooth chip. To resolve an issue like this it is best practice to check the PC's Bluetooth chipset manufacturer's website to see if they offer a firmware upgrade to update the firmware on the Bluetooth chipset to support the appropriate Bluetooth profiles (ie: A2DP) and then the computer will be compatible with the headset.
When a Bluetooth headset is being used in a non-standard application (ie: dictation) there can be functionality issues because this sort of application adds an additional level of inter-activity between devices/software. The Bluetooth headset is no longer interacting with just the device (ie: the computer) but is not also interacting with the software too. In some instances it is simply a matter adjusting the computer settings to allow the information (ie: microphone audio) get to the correct place (ie: dictation software). In other instances the it may be a situation where the hardware (ie: Bluetooth chip of the computer) is not designed to handle the intended functionality. For example some computers' Bluetooth chips will support audio output functions (ie: will output audio to the headphones for listening) but do not support audio input functions (ie: accept audio in from a microphone).
To resolve any compatibility, connectivity or functionality issues it needs to be determined where the issue is originating so that the underlying issue can be addressed. You can test many of these factors with a process of elimination by changing one aspect at a time. For example if you are having intermittent Bluetooth connectivity on one device (ie: computer) a good test is to connect the headphones to a different Bluetooth device (ie: cell phone). If the connectivity issues only occur on one device (ie: the computer) and not the other device (ie: the cell phone) then that would indicate that the headphones are fine and the issue is actually with the computer.
NOTE: If prompted for a password/PIN during the connection process the default number is "0000".
In situations where the device's (ie: computer's) built in Bluetooth chip does not support the appropriate Bluetooth profiles (ie: A2DP) or functionality (ie: not audio input) then the solution is to use a Bluetooth dongle (like the Sennheiser BTD 800) as it allows you to bypass the devices' built in Bluetooth chip and the dongle is set up with all the appropriate Bluetooth Profiles and functionality.