Alarms are a joke but I’d hide a kill switch someplace. And get a chain like this with the best lock you can find. NOT A MASTER!! I can pick them in seconds
ABUS 10KS 10' Maximum Security Square Chain and Sleeve - 3/8" Diameter Chain Link https://www.amazon.com/dp/B01N0R2BNW/ref=cm_sw_r_cp_api_glt_fabc_3Z9199XEPYRMNW349P7Y
What’s your budget? I’ve taken four bikes on a road trip (not to a music festival), on a hitch rack with a motorcycle chain running through the frames, around the tray rack, and secured with a padlock commensurate with the chain. I wouldn’t leave it like that in a big curry full of professional bike thieves, but it should be enough to deter your average festival goer.
Get a real chain like this
ABUS 10KS 10 Foot Maximum Security Square Chain and Sleeve - 3/8" Diameter Chain Link https://www.amazon.com/dp/B01N0R2BNW/ref=cm_sw_r_cp_api_glt_fabc_SYAADHD2FBRSJ9M2PZXV