Most of this stuff is "reasonably secure," but they're still radios, and the safest assumption is that someone is always listening.
The various wireless consortiums want everyone to believe wireless to be as (or more) secure than a connected phone. Even the original 900 mhz cell phone was promoted as a secure system: the consortium even got some (really stupid) laws passed to make it illegal to listen in..... and you could monitor those with an old unmodified TV set. Even common scanners these days can do "trunk tracking," so frequency hopping is no big deal. Trunk systems are not radically different than the systems used for wireless phones.
The test equipment used to repair and test this equipment is expensive but available; on an equipment lease or rental , it's not too bad and some "bad guys" could monitor. It's strictly an issue of effort versus return. There isn't much effort in listening, and in a wireless-saturated area, the payoff might be worth it.
How many college students are ordering food for delivery and giving a CC for payment? The likelyhood of a "payoff" by listening is growing; IMHO, it won't be much longer before we hear about someone stealing information over the new wireless systems.
Bottom line: Regardless of the form factor, they're still radios. Radios can be intercepted. With the right motivation, encryption can be broken (note: all the DirecTV pirates that have cracked the last 4 generations of "unbreakable encryption" conditional access cards).
Be careful.
FWIW
Scott