Have just had a solar battery installed in my garage. suggestions for best alarm

The "best alarm" is one that you like the look of, is easy to install, and you are happy with the price.

That aside, a smoke alarm in a garage is not a lot of use if it is the only one you have, if it should activate and you are all asleep chances are you will not hear it, so I would suggest you buy a smoke alarm that is compatible with what you already have. If you have no other smoke detectors buy some that are interlinkable either by hardwire or radio. Radio interlinked cost more, but you save on disruption and time. You should have a minimum of an alarm on each level and one adjacent any other sleeping areas if required.

By best I meant type. As there will be smoke when I drive in and out for a short period, I don't want it going off for no  reason

Any smoke alarm can be activated by car exhaust, might not happen every time but it can and will happen, it would also depend on what exactly your car emits, you may want to try optical smoke alarm, but also as I said get interlinked alarms and have another on the landing.

On 31/05/2023 at 19:42, dst said:

By best I meant type. As there will be smoke when I drive in and out for a short period, I don't want it going off for no  reason

A heat alarm would be better suited in a garage environment.

It should be a heat detector NOT a smoke (unless the solar gear is in a separate room or large cupboard in the garage where you could fit a smoke without cars setting it off)  . Your garage ,if directly connected to the house, should have a fire door and fire resistant walls anyway so the difference in response time between a heat and a smoke shouldn't be critical