This might be more than you want to spend but it sounds like it will meet your needs but I haven't seen it or know anyone who has one.
Secure your camp site day or night. While you are away know you site is protected from hungry animals, thieves, or any other unwanted guests. Arm the CAMPSAFE when you leave and it will blanket the campsite (400sg.ft.) with a invisible rf signal. Any violation of this perimeter will cause the siren to blast away. Can be heard over a mile away. When night falls arm the campsafe l with one of the remotes after you turn in. Simply disarm it if you need to exit the tent. Set it close to your tent or tents to prevent unwanted visitors while you are sleeping. Any movement which breaks the barrier will sound the siren and light up the night with the hyper strobe. Nothing on the market exists until now that offers you this protection. Self contained portable security system. Move it around the site as needed. Protect yourself from thieves and intruders with steal armors CAMPSAFE alarm. Weights less than 10lbs. Rechargeable battery will last a whole week without charging.Skin CAMPSAFEin an ingloo cooler for additional protection as well as a way to make it invisible from detection.
CAMPSAFE
Features:
· Built-in 120db siren
· On-board Shock Sensor
· 400 sq.ft. Coverage with RF Sensor
· Alarm sounds 30sec and resounds if violation continues
· 12volt recharge able sealed 3.4ah battery
· Master KEY STYLE ON/OFF Switch
· 2) 3 button key fobs
· Mounted additional siren connectors
· Smart Battery Charger
· Weather Resistant Housing
· Flashing LED
· 7 day operate with full charge
· Will operate when covered with non-metallic housing or cover
· SIZE: 12¾ x 5¼ Shipping weight 10lbs
· 1 year replacement warranty
· PRICE $450.00 MSRP
http://www.campingalarms.com/index.html