This is John Allender's 2nd counterfeit U.S. coin detector with 6 counterfeit gold coins to detect, $1, $2.50, $3, $5, $10, and $20. The Patent number is 13,840 and dated November 27, 1855. There are a few variations of this model with different stamps.

This is a rocker style detector with a small bottom stand. You place the coin flat in the slot for weight balance detection, and between the narrow gap for a diameter check. This was a relatively simple detector that was effective and popular in the mid-19th century. Overall condition is very fine.