In general you should obtain a permit for such updates since local authorities may want to make sure that your smoke and fire detector upgrade has been properly performed by a professional. They may also wish to perform an inspection in your warehouse to ensure that smoke alarm and fire alarm installation conforms to locally approved and applicable code.
However, permit, inspection, and installation rules (performed by a licensed professional or not) may vary significantly between jurisdictions. You may not need a permit at all so it’s best to make a phone call to your local department of permits.
There’s one more thing to keep in mind. If you have any insurance coverage on your building and on whatever you store in this warehouse it might be wise to produce some paperwork trail associated with smoke alarm and fire detector update. You should keep that in a safe place in case of an accident. Notifying local authorities would provide just that.
This would ensure that in case of a fire your insurance provider doesn’t refuse to cover damages because your fire / smoke alarm wasn’t up to the current code (in reality it was but nobody knew about it)… just a thought.