I made my own cell phone trigger. It works great and cost about $300 for everything including solar panel and high end lithium battery
I would like more details on your set up please.
It's been a while since I built it but the main component and most expensive part can be found on Amazon https://www.amazon.com/KiaoTime-GSM-RELAY-US4G-Output-Control-Contact/dp/B01MZ0VFAA
You will need to get an AT&T prepaid data plan that runs $25 for three months and can be renewed before it expires. It will have the sim card. The controler will have to be configured to only accept calls and texts from your phone number so that sales calls don't trigger it.
The trigger can be any electronic trunk release or use an actuator like this depening on how you have your trap door release setup.
The solar panel, Solar panel controller waterproof box to contain all the electronics and battery can all be gotten from amazon.
Advice... Make sure you use solid copper wires. The copper coated wires will corrode outdoors very fast and will frustrate you when they do corrode.