I do have to say the support I've gotten from spider robitics on our herp stats has been excellent. I get better support on my $300 Herpstat pros than I do from most breeders on snakes that cost more.

As far as back up Thermostats go though, I use a Ranco. If it is only controlling one enclosure I place the probe on the same heating element and set it to shut the Herpstat off if temps get 2 degrees above the herpstat setting. In a rack I use the same setting but I put it on another heating element in the rack. As far as to cold goes the only reasonable way to go would be setting up a T-stat to sound an alarm if the temp drops 2 degrees below the herpstat setting as you can not have two different T-stats feeding a heat strip in parallel as this could cause damage to electronic proportional controlled T-stats like the Herpstat.

If your really crazy as I am with my incubator I use a Herpstat to proportionally control the temp and hold at 88 degrees. Then I have a secondary heating element on a Ranco set at 86 degrees. Then I have a second Ranco, third T-stat, set so it shuts both heating elements off if temperatures hit 90 degrees. Also if either ranco goes off an alarm buzzer will sound. In the 4 months I've had my incubator on the only time the buzzers have went off was during initial set up testing When I purposefully unplugged the Herpstat to let temps drop or set the Herpstat to a temp higher than the high set Ranco.