Roy J. Snell 
Whispers at Dawn [PDF ebook] 
Or, The Eye

Amateur detective and all-around good guy Johnny Thompson has always relied on his athletic prowess and quick wits to help him crack the cases he stumbles across. But in this volume of the series, our hero gets a little help from some cool technological gadgets and gizmos. Whispers at Dawn will give younger readers a glimpse into the past with its descriptions of the cutting-edge electronics of the early twentieth century.