Beacons are ready to work outdoors: they’re splashproof and dustproof, so go ahead and place them in your yard.
However, keep in mind that they're not 100% waterproof. If water gets under the adhesive backing, it can kill the PCB. Also, heavy rain can also affect signal propagation.
Optimal operating temperature for the battery is 23°C (73°F). Extreme temperatures--over 60°C (140°F) or below -10°C (14°F)--can reduce battery life.