160 characters is the limit for standard text messaging. Omnilert sends standard texts so that your messages can be received on all major US carriers. As such, 160 characters is the maximum length sent for SMS.
When composing a message, there will be a character counter at the bottom of the composer window to indicate the characters remaining for your message.
Note: If a text message exceeds 160 characters (or includes non-standard characters), the Omnilert system will automatically insert a short URL (link) to view the full message in a browser.