This X-Sense smart mailbox alarm is $30, well below its 90-day Amazon average of $41. The kit includes the SBS50 base station, which can connect up to 50 X-Sense devices.
The alarm works with curbside, wall mount, slot, and cluster mailboxes, but not mail slots without lids. Shipping is free.
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Features real-time app alerts compatible with most mailboxes 4-year battery life long-range WiFi connection