Omnilert's shortcode gateway routes to all major US mobile providers. So, if you've changed carriers between major US carriers (AT&T to Verizon or vice versa), your service will likely just forward automatically.
However, you can test your ability to receive short code texts by texting TEST to 79516. If you receive a response message from Omnilert, then you should be OK going forward. No action should be needed.
If you do not receive a response to TEST, then please check with your new carrier to ensure that your number is fully ported to their network, registered with all aggregator gateways, and allowed to receive short code SMS texts.